CN113848365A - Circuit for measuring phase current of motor in high bandwidth - Google Patents
Circuit for measuring phase current of motor in high bandwidth Download PDFInfo
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- CN113848365A CN113848365A CN202111431389.1A CN202111431389A CN113848365A CN 113848365 A CN113848365 A CN 113848365A CN 202111431389 A CN202111431389 A CN 202111431389A CN 113848365 A CN113848365 A CN 113848365A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
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Abstract
The invention discloses a circuit for measuring motor phase current with high bandwidth, which can solve the problem that the measured signal with small amplitude can quickly and obviously inhibit common mode interference in a very short time due to the interference and instability of the measured signal generated by the step change of a large-amplitude common mode signal when a motor driving circuit generates a pulse width modulation signal, keep the stability of the signal, avoid time delay caused by the influence of sudden step and greatly improve the speed of current measurement so as to improve the bandwidth of the sudden step current measured by a system.
Description
Technical Field
The invention relates to a circuit for measuring phase current of a direct current brushless motor, in particular to a circuit for measuring phase current of a motor, which has high bandwidth, high speed and quick response.
Background
Although the development time of the brushless direct current motor in China is short, the brushless direct current motor is rapidly developed along with the increasing maturity and perfection of the technology, and is widely applied to fields of aeromodelling, medical equipment, household appliances, electric vehicles, aerospace, aviation and the like. In recent years, brushless dc motors are gradually entering other fields due to the increase of energy production and the decrease of price, and are continuously entering various application scenes in production and life. Meanwhile, the requirements on the design indexes and performance parameters of the brushless direct current motor are higher and higher, the purposes of more accurate torque control, higher-precision phase current measurement, more accurate motor rotating speed control and the like are achieved by continuously optimizing the design of the motor, but the speed of phase current measurement is often ignored, even the bandwidth parameters of the system measured phase current are even, and the requirements on high bandwidth of the measured phase current are very important in fields requiring high performance, such as the aerospace field.
Disclosure of Invention
In order to improve the speed of measuring the phase current and improve the bandwidth performance of the system for measuring the phase current, the invention introduces a signal common mode rejection module on the basis of the prior art, can effectively improve the measuring speed of the phase current and provides a circuit for measuring the motor phase current with high bandwidth.
A circuit for high bandwidth measurement of motor phase current, comprising: the phase current feedback signal acquisition module, the signal common mode rejection module and the signal acquisition processing and calculating module, wherein the signal common mode rejection module is connected to the output end of the phase current feedback signal acquisition module, and the signal acquisition processing and calculating module is connected to the output end of the signal common mode rejection module.
Preferably, the acquisition module of the phase current feedback signal comprises a first resistor, one end of the first resistor is connected with a motor driving signal, the other end of the first resistor is connected with a load, the motor driving signal sends a signal a to the first resistor, and the first resistor sends a signal b to the load.
Preferably, the signal common mode rejection module includes a first operational amplifier, a first capacitor, a second resistor, a third resistor, and a fourth resistor; one end of the first capacitor is connected with the signal a, and the other end of the first capacitor is connected with the positive input end of the first operational amplifier; one end of the second resistor is connected with the signal b, and the other end of the second resistor is connected with the negative input end of the first operational amplifier; one end of the third resistor is connected with a ground signal, and the other end of the third resistor is connected with the positive input end of the first operational amplifier; one end of the fourth resistor is connected with the negative input end of the first operational amplifier, and the other end of the fourth resistor is connected with the output end of the first operational amplifier.
Preferably, the processing and calculating module for the collected signal comprises a processor, a third operational amplifier, an eighth resistor, a ninth resistor and a tenth resistor; one end of the eighth resistor is connected with the output signal of the first operational amplifier, and the other end of the eighth resistor is connected with the positive input end of the third operational amplifier; one end of the ninth resistor is connected with the output signal of the second operational amplifier, and the other end of the ninth resistor is connected with the negative input end of the third operational amplifier; one end of the tenth resistor is connected with the negative input end of the third operational amplifier, and the other end of the tenth resistor is connected with the output end of the third operational amplifier; and the output end of the third operational amplifier is connected with an analog-digital conversion interface of the processor.
The circuit for measuring the phase current of the motor with high bandwidth adopts the signal common mode rejection module, ensures that the output signal of the first operational amplifier, the output signal of the second operational amplifier and the current feedback signal are not unstable due to the abrupt step common mode interference of the signal a and the signal b, avoids time delay, greatly improves the current measurement rate, and accordingly improves the bandwidth of the system for measuring the current.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a block diagram of the modular design of the circuit of the present invention;
FIG. 2 is a schematic diagram of a module for acquiring phase current feedback signals according to the present invention;
FIG. 3 is a schematic diagram of a common mode rejection module for signal a according to the present invention;
FIG. 4 is a schematic diagram of a common mode rejection module for signal b according to the present invention;
fig. 5 is a schematic diagram of a processing and calculating module for collecting signals according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the circuit implementation of the present invention includes: the device comprises a phase current feedback signal acquisition module, a signal common mode rejection module and a signal acquisition processing and calculating module, wherein the connection relation among the modules is shown in figure 1, and the phase current feedback signal acquisition module can acquire a voltage signal of a motor coil driving signal; the signal common mode rejection module can ensure that the acquired voltage signals are not subjected to common mode interference of abrupt step, and the voltage signals are kept stable in a very short time, so that the acquired voltage signals are ensured to be in a real and effective state; the collected signal processing and calculating module can collect real and effective voltage signals at the first time, preprocess the voltage signals, ensure that an analog-digital conversion interface of the processor can process and calculate, obtain a phase current value, realize the rapid measurement of the phase current and improve the bandwidth of the system for measuring the phase current.
The phase current feedback signal acquisition module is designed to be composed of a first resistor, and as shown in fig. 2, the working principle is as follows: the motor driving signal is connected with a load (a motor coil) to provide a required current signal for the normal work of the motor, and the driving signal must be continuously switched between high and low levels due to the time sequence requirement of each phase of driving signal of the brushless direct current motor, and the high level voltage values required by different motors are different, generally speaking, the voltage amplitude of the high level is 30 volts, and the voltage amplitude of the low level is 0 volt; in order to collect a current signal, a first resistor is inserted into a driving circuit, that is, one end of the first resistor is connected with a motor driving signal, and the other end of the first resistor is connected with a load (a motor coil), at this time, because the current in the driving circuit flows through the first resistor, a signal a and a signal b are generated at two ends of the first resistor, and are used as input signals of a signal common mode rejection module, the phase current is calculated through the difference value of voltages at the two ends, and the function of current feedback is realized, and the relational expression of the signal a and the signal b is as follows:
signal a voltage value-signal b voltage value = phase current value ×. first resistance value;
the signal common mode rejection module is designed to be composed of a first operational amplifier, a first capacitor, a second resistor, a third resistor and a fourth resistor, and as shown in fig. 3, the working principle is as follows:
case 1: when the motor driving signal is at a low level (the voltage amplitude is 0 v), that is, the signal a is at a low level, due to the presence of the third resistor and the ground signal (the voltage amplitude is 0 v), the amplitudes of the voltages at the positive input end and the negative input end of the first operational amplifier are 0 v, at this time, the amplitude of the output signal of the first operational amplifier at the output end of the first operational amplifier is also 0 v, that is, the amplitude of the output signal of the first operational amplifier = 0 v;
case 2: when the motor driving signal is converted from low level to high level (the voltage amplitude is suddenly stepped from 0 volt to 30 volts), the signal a is also converted from low level to high level along with the motor driving signal, the suddenly stepped signal a reaches the positive input end and the negative input end of the first operational amplifier through the first capacitor and the second resistor respectively, at this time, the second resistor, the fourth resistor and the first operational amplifier form a differential operational amplifier circuit (the differential operational amplifier circuit has the function of subtracting the voltage amplitudes of the signals at the positive input end and the negative input end and amplifying according to a certain multiple, the amplification multiple in the circuit is the fourth resistor/the second resistor), because the positive input signal and the negative input signal keep consistent change in the whole process, namely the difference of the voltage amplitudes of the positive input end and the negative input end is 0 volt, the amplitude of the output signal of the first operational amplifier at the output end of the first operational amplifier is 0 volt, i.e. the amplitude of the first operational amplifier output signal = 0 volts;
case 3: when the motor driving signal is at a high level (the voltage amplitude is 30 v), the signal a is at a high level, and at this time, the signal a reaches the negative input end of the first operational amplifier through the second resistor, but cannot reach the positive input end of the first operational amplifier through the second capacitor (the signal a is at a level that is fixed and unchanged by direct current, and the capacitor has an effect of isolating the direct current level), at this time, the first operational amplifier, the second resistor, the third resistor and the fourth resistor constitute a reverse amplification circuit, and the signal a is converted into an output signal of the first operational amplifier, and the specific relation formula is as follows:
the amplitude of the first operational amplifier output signal = -the voltage amplitude of signal a = -fourth resistor/second resistor.
Case 4: when the motor driving signal is converted from high level to low level, the circuit operation principle and process are the same as those of case 2, and at this time,
the amplitude of the first operational amplifier output signal = 0 volts;
thereafter, the change in signal a repeats the cycle of case 1, case 2, case 3, and case 4.
The signal b, like the signal a, also passes through the signal common mode rejection module, as shown in fig. 4, and the analysis process is also the same as the signal a, which is not described again.
The circuit design of the collected signal processing and calculating module is composed of a processor, a third operational amplifier, an eighth resistor, a ninth resistor and a tenth resistor, as shown in fig. 5, the schematic diagram of the collected signal processing and calculating module is as follows: the third operational amplifier, the eighth resistor, the ninth resistor and the tenth resistor form a differential operational amplifier, and an output end signal (namely, a current feedback signal) and a positive and negative input end signal (namely, an output signal of the second operational amplifier and an output signal of the first operational amplifier) of the third operational amplifier satisfy the following conditions:
the voltage amplitude of the current feedback signal = (second operational amplifier output signal amplitude-first operational amplifier output signal amplitude) × tenth resistance value/eighth resistance value;
wherein the eighth resistance value = the ninth resistance value;
then, the current feedback signal is connected to an analog-digital conversion interface of the processor, and the phase current is calculated.
In case 1 (the motor driving signal is at a low level, the phase current is 0), the amplitude of the output signal of the first operational amplifier = 0 v, the amplitude of the output signal of the second operational amplifier = 0 v, and at this time, the amplitude of the current feedback signal = 0 v;
in case 2 (the motor driving signal is converted from low level to high level to generate common mode interference, and the signal a is interfered by 30 v), the following conditions are satisfied:
the amplitude of the first operational amplifier output signal = 0 volts, and the amplitude of the second operational amplifier output signal = 0 volts;
at this time, the current feedback signal amplitude = 0 volts, noting that: the amplitude of the current feedback is not affected by the common-mode interference;
in case 3 (the motor driving signal is at a high level, and the phase current is in a steady state), the following conditions are satisfied:
the amplitude of the output signal of the first operational amplifier = -the amplitude of the signal a = -the fourth resistor/the second resistor;
the amplitude of the second operational amplifier output signal = -the amplitude of signal b = -seventh resistor/fifth resistor;
wherein, the fifth resistance value = the second resistance value, and the seventh resistance value = the fourth resistance value;
at this time, the following are satisfied:
current feedback signal amplitude = (fourth resistance value/second resistance value) × (signal a amplitude-signal b amplitude) × (tenth resistance value/eighth resistance value);
wherein, signal a voltage value-signal b voltage value = phase current value ×. first resistance value;
the relation becomes:
current feedback signal amplitude = (fourth resistance value/second resistance value) × (phase current value × first resistance value) × (tenth resistance value/eighth resistance value);
therefore:
phase current value = current feedback signal amplitude value (second resistance value/fourth resistance value) x (eighth resistance value/tenth resistance value)/first resistance value;
the first resistance value, the second resistance value, the fourth resistance value, the eighth resistance value and the tenth resistance value are known design parameters, and the amplitude of the current feedback signal needs to be acquired and read through an analog-digital conversion interface of the processor.
Note that due to the existence of the signal common mode rejection module, the signals (the first operational amplifier output signal, the second operational amplifier output signal and the current feedback signal) can quickly enter a stable state, and are not affected by the common mode interference like the signal a and the signal b and are in an unstable state (the unstable state can last for a certain time, which causes a certain time delay and reduces the bandwidth of the phase current measured by the system), so that the phase current can be quickly measured, and the bandwidth performance of the phase current measured by the system can be effectively improved.
In case 4 (the motor driving signal is converted from high level to low level), the circuit operation principle and the analysis process are the same as those in case 2, and are not described herein again.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (4)
1. A circuit for high bandwidth measurement of phase current in an electric motor, comprising: the phase current feedback signal acquisition module, the signal common mode rejection module and the signal acquisition processing and calculating module, wherein the signal common mode rejection module is connected to the output end of the phase current feedback signal acquisition module, and the signal acquisition processing and calculating module is connected to the output end of the signal common mode rejection module.
2. The circuit for high bandwidth measurement of motor phase current of claim 1, wherein: the acquisition module of the phase current feedback signal comprises a first resistor, one end of the first resistor is connected with a motor driving signal, the other end of the first resistor is connected with a load, the motor driving signal sends a signal a to the first resistor, and the first resistor sends a signal b to the load.
3. The circuit for high bandwidth measurement of motor phase current of claim 2, wherein: the signal common mode rejection module comprises a first operational amplifier, a first capacitor, a second resistor, a third resistor and a fourth resistor; one end of the first capacitor is connected with the signal a, and the other end of the first capacitor is connected with the positive input end of the first operational amplifier; one end of the second resistor is connected with the signal b, and the other end of the second resistor is connected with the negative input end of the first operational amplifier; one end of the third resistor is connected with a ground signal, and the other end of the third resistor is connected with the positive input end of the first operational amplifier; one end of the fourth resistor is connected with the negative input end of the first operational amplifier, and the other end of the fourth resistor is connected with the output end of the first operational amplifier.
4. The circuit for high bandwidth measurement of motor phase current of claim 1, wherein: the acquisition signal processing and calculating module comprises a processor, a third operational amplifier, an eighth resistor, a ninth resistor and a tenth resistor; one end of the eighth resistor is connected with the output signal of the first operational amplifier, and the other end of the eighth resistor is connected with the positive input end of the third operational amplifier; one end of the ninth resistor is connected with the output signal of the second operational amplifier, and the other end of the ninth resistor is connected with the negative input end of the third operational amplifier; one end of the tenth resistor is connected with the negative input end of the third operational amplifier, and the other end of the tenth resistor is connected with the output end of the third operational amplifier; and the output end of the third operational amplifier is connected with an analog-digital conversion interface of the processor.
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