CN112688603A - High-precision brush motor current loop control method - Google Patents
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Abstract
The invention discloses a high-precision brush motor current loop control method in the field of servo motor control, which comprises the following steps: step 1: acquiring two-phase current signals of the motor at a set sampling moment; step 2: carrying out mean value processing on the two-phase current signals to obtain intermediate value current; and step 3: calculating the average current of any phase current of the motor in a PWM chopping period; and 4, step 4: repeating the steps 1-3 for N times, and calculating to obtain a corresponding relation between the average current and the median current; and 5: determining a model parameter of the motor through parameter identification, designing a control rule of output voltage, and introducing a speed compensation term, a feedforward reference compensation term, a proportional error term and an integral feedback term; step 6: and (5) equating the control voltage value of the motor to be a duty ratio and controlling the operation of the motor. The invention obviously improves the response speed of the current loop, improves the response capability of the loop on the premise of not influencing the current control precision, and further improves the control efficiency of the system.
Description
Technical Field
The invention relates to the field of servo motor control, in particular to a high-precision brush motor current loop control method.
Background
The current loop control of the motor plays a very important role in the servo closed-loop control, the phase current is generally required to be sampled based on the control method of the brush motor phase current, for a large-inductance motor, the phase current of the motor changes relatively slowly, and the phase current fluctuation in a PWM control period is generally very small, so that the requirement on the sampling moment of the current is not high, and the requirement on the closed-loop control is easily met; however, for a high-efficiency motor, the phase inductance of the motor is small, the phase current output of the motor is very close to the supply voltage waveform, and is in a square wave state, and the change of the current in one PWM control period is very large, which results in very short time for sampling the current, which makes it difficult to complete the sampling of the motor current and to realize the closed-loop control of the current.
The existing current loop control technology has the following defects: (1) the current sampling time is random, so that the current error between the current control and the actual requirement is large; (2) based on the traditional PID control method, the controlled object information cannot be utilized, and the accuracy and the efficiency of control are low.
Disclosure of Invention
The invention aims to provide a high-precision brush motor current loop control method to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme:
a high-precision brush motor current loop control method comprises the following steps:
step 1: setting a fixed sampling moment, and acquiring two-phase current signals of the motor;
step 2: carrying out mean value processing on the two-phase current signals to obtain intermediate value current;
and step 3: calculating the average current of any phase current of the motor in a PWM chopping period;
and 4, step 4: repeating the steps 1-3 for N times, and calculating to obtain a corresponding relation between the average current and the median current;
and 5: obtaining feedback current and a proportional coefficient according to the relational expression, determining a model parameter of the motor through parameter identification, designing a control rule of output voltage according to the model parameter, and introducing a speed compensation term, a feedforward reference compensation term, a proportional error term and an integral feedback term which are obtained through calculation according to the model parameter, the feedback current and the proportional coefficient into the control rule;
step 6: and equating the calculated control voltage value of the motor to be a duty ratio, and controlling the operation of the motor according to the duty ratio.
As a modified scheme of the invention, the step 1 comprises the following steps:
step 1.1: giving the motor a predetermined voltage um；
Step 1.2: setting the sampling time of the current as the underflow interrupt time of PWM through a digital chip;
step 1.3: acquiring digital values N corresponding to two current sampling channels of the motorxAnd a corresponding digital value M when the current is zerox，x＝a,b；
Step 1.4: the current two-phase current signal value of the motor is obtained by calculation as follows: i.e. ix＝ki(Nx-Mx)＝kiNx-kiMx，kiIs a scale factor for digital to analog conversion.
As an improvement of the present invention, in step 2, the formula for calculating the median current is:
ia、ibrespectively two-phase current signals.
As an improvement of the present invention, in step 4, the relation is: i.e. im＝kcimid+bcWherein i ismRepresents the average current imidRepresenting the median current, kc、bcAll represent proportionality coefficients, and the calculation formula is as follows:
as a modified scheme of the invention, the step 5 comprises the following steps:
step 5.1: obtaining phase resistance R, phase inductance L and back electromotive force coefficient k of the motor through parameter identificationeAnd given a reference current irefThe angular velocity omega of the motor;
step 5.2: calculating to obtain the actual feedback current if，if＝kcimid+bc；
Step 5.3: calculating a reference current irefThe derivative of (a) of (b),
iref_pre、irefrespectively representing a previous value and a current value of the reference current, and delta T represents a time difference between the previous value and the current value;
step 5.4: calculating a velocity compensation term usFeedforward reference compensation term uFFProportional error term upIntegral feedback term uiWherein u iss＝keω；
up＝kp(if-iref)，kpIs a scale factor; u. ofi＝ui+kI(if-iref) dt, and uimin<ui<uimax，uimin、uimaxIs the upper and lower limits of the amplitude, kIIs an integral scale factor;
step 5.5: the reference value of the last time of updating is: i.e. iref_pre＝iref；
Step 5.6: the control rule of the output voltage obtained by calculation is as follows: u-us+uFF+up+uiAnd the width limit of the output voltage u is: u. ofmin<u<umax。
AsAccording to a further development of the invention, step 6, the duty cycle δdutyExpressed as:
Vsand is expressed as the supply voltage of the direct current bus of the motor inverter bridge.
Has the advantages that: aiming at a model of the motor, the speed compensation term and the feedforward reference compensation term of the motor are introduced into a control rule, so that the response speed of a current loop is obviously improved; meanwhile, a proportional error term and an integral feedback term are introduced, so that the arbitrary convergence rate of the current loop can be adjusted theoretically, and meanwhile, the control precision of the current loop can be improved, so that the response capability of the loop is improved on the premise that the control precision of the current is not influenced, and the control efficiency of the system is improved.
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FIG. 1 is a flow chart of the steps of the present invention;
FIG. 2 is a flow chart of steps of an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be 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 of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a method for controlling a current loop of a high-precision brush motor includes the following steps:
step 1: setting a fixed sampling time to acquire two-phase current signals of a motor aiming at the problem that the current sampling time is random in the existing current loop control technology;
specifically, step 1 comprises:
step 1.1: giving the motor a predetermined voltage um；
Step 1.2: setting the sampling time of the current as the underflow interrupt time of PWM through a digital chip;
step 1.3: acquiring digital values N corresponding to two current sampling channels of the motorxAnd a corresponding digital value M when the current is zeroxX is a, b; the phase current signals are converted into voltage signals through sampling resistors in the sampling channels, and the voltage signals are converted into clean voltage signals which can be identified by A/D through filtering and amplification processing for subsequent use.
Step 1.4: the current two-phase current signal value of the motor is obtained by calculation as follows: i.e. ix＝ki(Nx-Mx)＝kiNx-kiMx，kiIs a scale factor for digital to analog conversion.
Step 2: and (3) carrying out mean value processing on the two-phase current signals to obtain a median current, wherein the calculation formula of the median current is as follows:
ia、ibrespectively two-phase current signals.
And step 3: observing the phase current waveform of any phase of the motor through an oscilloscope, and calculating the average current i of the phase current in a PWM chopping periodm*；
And 4, step 4: repeating the steps 1-3N times to obtain an average current im1～imNWith corresponding intermediate value current imid1～imidNAnd calculating the corresponding relation between the average current and the median current as follows:
im＝kcimid+bc
wherein k isc、bcAll of which represent the scaling factors, are,
here, the more the number of repetitions is, the larger the calculation base of the relational expression is, and the higher the fitting accuracy of the curve corresponding to the relational expression to the actual current sample is.
And 5: obtaining feedback current and a proportional coefficient according to the relational expression, determining a model parameter of the motor through parameter identification, designing a control rule of output voltage according to the model parameter, and introducing a speed compensation term, a feedforward reference compensation term, a proportional error term and an integral feedback term which are obtained through calculation according to the model parameter, the feedback current and the proportional coefficient into the control rule; the speed compensation term is mainly used for compensating error offset caused by the rotating speed of the motor, the feedforward reference compensation term is used for compensating static inherent deviation caused by reference current, the proportional error term is used for improving the dynamic response rapidity of error compensation, and the integral term is used for eliminating the steady-state error of current; specifically, step 5 comprises:
step 5.1: obtaining phase resistance R, phase inductance L and back electromotive force coefficient k of the motor through parameter identificationeAnd given a reference current irefThe angular speed omega of the motor rotor;
step 5.2: calculating to obtain the actual feedback current if，if＝kcimid+bc；
Step 5.3: calculating a reference current irefThe derivative of (a) of (b),
iref_pre、irefrespectively representing a previous value and a current value of the reference current, and delta T represents a time difference between the previous value and the current value; the reference current of the motor is determined from the speed loop output.
Step 5.4: calculating a velocity compensation term usFeedforward reference compensation term uFFProportional error term upIntegral feedback term uiWherein u iss＝keω；uFF＝Riref+Liref；up＝kp(if-iref)，kpIs a scale factor; u. ofi＝ui+kI(if-iref) dt, and uimin＜ui＜uimax，uimin、uimaxUpper and lower limits of amplitude for saturation limiting of the integral phase according to actual requirements of the inverted output, kIIs an integral scale factor;
step 5.5: the reference value of the last time of updating is: i.e. iref_pre＝iref
Step 5.6: the control rule of the output voltage obtained by calculation is as follows: u-us+uFF+up+uiAnd the width limit of the output voltage u is: u. ofmin＜u＜umax。
Step 6: the calculated control voltage value of the motor is equivalent to a duty ratio deltadutyExpressed as:
Vsthe control method is characterized in that the control method is represented as a motor inverter bridge direct current bus supply voltage, and the operation of a motor is controlled according to a duty ratio.
Aiming at a model of the motor, the speed compensation term and the feedforward reference compensation term of the motor are introduced into a control rule, so that the response speed of a current loop is obviously improved; meanwhile, a proportional error term and an integral feedback term are introduced, so that the arbitrary convergence rate of the current loop can be adjusted theoretically, and meanwhile, the control precision of the current loop can be improved, so that the response capability of the loop is improved on the premise that the control precision of the current is not influenced, and the control efficiency of the system is improved.
Although the present description is described in terms of embodiments, not every embodiment includes only a single embodiment, and such description is for clarity only, and those skilled in the art should be able to integrate the description as a whole, and the embodiments can be appropriately combined to form other embodiments as will be understood by those skilled in the art.
Therefore, the above description is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application; all changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Claims (6)
1. A high-precision brush motor current loop control method is characterized by comprising the following steps:
step 1: setting a fixed sampling moment, and acquiring two-phase current signals of the motor;
step 2: carrying out mean value processing on the two-phase current signals to obtain intermediate value current;
and step 3: calculating the average current of any phase current of the motor in a PWM chopping period;
and 4, step 4: repeating the steps 1-3 for N times, and calculating to obtain a corresponding relation between the average current and the median current;
and 5: obtaining feedback current and a proportional coefficient according to the relational expression, determining a model parameter of the motor through parameter identification, designing a control rule of output voltage according to the model parameter, and introducing a speed compensation term, a feedforward reference compensation term, a proportional error term and an integral feedback term which are obtained through calculation according to the model parameter, the feedback current and the proportional coefficient into the control rule;
step 6: and equating the calculated control voltage value of the motor to be a duty ratio, and controlling the operation of the motor according to the duty ratio.
2. The method for controlling the current loop of the high-precision brush motor according to claim 1, wherein the step 1 comprises the following steps:
step 1.1: giving the motor a predetermined voltage um；
Step 1.2: setting the sampling time of the current as the underflow interrupt time of PWM through a digital chip;
step 1.3: acquiring digital values N corresponding to two current sampling channels of the motorxAnd a corresponding digital value M when the current is zerox，x＝a，b；
Step 1.4: the current two-phase current signal value of the motor is obtained by calculation as follows: i.e. ix＝ki(Nx-Mx)＝kiNx-kiMx，kiIs a scale factor for digital to analog conversion.
3. The method for controlling the current loop of the high-precision brush motor according to claim 2, wherein in the step 2, the stepThe formula for calculating the interval current is as follows:
ia、ibrespectively two-phase current signals.
4. A high precision brush motor current loop control method according to claim 1, 2 or 3, characterized in that in step 4, the relation is: i.e. im＝kcimid+bcWherein i ismRepresents the average current imidRepresenting the median current, kc、bcAll represent proportionality coefficients, and the calculation formula is as follows:
5. the method for controlling the current loop of the high-precision brush motor according to claim 4, wherein the step 5 comprises the following steps:
step 5.1: obtaining phase resistance R, phase inductance L and back electromotive force coefficient k of the motor through parameter identificationeAnd given a reference current irefThe angular speed omega of the motor rotor;
step 5.2: calculating to obtain the actual feedback current if，if＝kcimid+bc；
Step 5.3: calculating a reference current irefThe derivative of (a) of (b),
iref_pre、irefrespectively representing a previous value and a current value of the reference current, and delta T represents a time difference between the previous value and the current value;
step 5.4: calculating a velocity compensation term usFeedforward reference compensation term uFFProportional error term upIntegral feedback term uiWherein u iss＝keω；
up＝kp(if-iref)，kpIs a scale factor; u. ofi＝ui+kI(if-iref) dt, and uimin＜ui＜uimax，uimin、uimaxIs the upper and lower limits of the amplitude, kIIs an integral scale factor;
step 5.5: the reference value of the last time of updating is: i.e. iref_pre＝iref；
Step 5.6: the control rule of the output voltage obtained by calculation is as follows: u-us+uFF+up+uiAnd the width limit of the output voltage u is: u. ofmin＜u＜umax。
6. A high precision brush motor current loop control method according to claim 5, characterized in that in step 6, the duty ratio δdutyExpressed as:
Vsand is expressed as the supply voltage of the direct current bus of the motor inverter bridge.
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