CN110208592B - Three-phase current sampling method of three-phase motor - Google Patents
Three-phase current sampling method of three-phase motor Download PDFInfo
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Abstract
The invention provides a three-phase current sampling method of a three-phase motor, which takes equivalent impedance introduced by a connecting circuit and the like between sampling resistors into consideration, obtains the actual value of each phase offset voltage according to the voltage drop at two ends of the equivalent impedance, and finally obtains the actual voltage drop at two ends of each sampling circuit according to the actual value of each phase offset voltage, thereby more accurately sampling the three-phase current of the three-phase motor.
Description
Technical Field
The invention belongs to the technical field of current sampling, and particularly relates to a three-phase current sampling method of a three-phase motor.
Background
The early motor control uses open loop control, does not detect the position information or the current information of the motor, and has the defects of low control efficiency, slow response speed, poor control precision and the like. With the development of power electronics and integrated circuits, closed-loop control of motors has become a common algorithm in the industry.
The closed-loop control of the motor usually comprises a current closed loop, a rotating speed closed loop and a position closed loop from inside to outside, and for a general motor controller, only the current closed loop and the rotating speed closed loop are included; for the servo controller, besides a current closed loop and a rotating speed closed loop, a position closed loop is also included. In general, a motor controller or a servo controller needs a current closed loop.
The closed-loop control is to collect the actual current as the feedback current, and perform closed-loop operation after making a difference according to the feedback current and a given value so as to eliminate the error between the given value and the feedback value and achieve the purpose that the feedback current tracks the given current in real time.
The feedback current is the actual current, and the accurate control of the current can be achieved only by accurately sampling the actual current. A sampling resistor is connected in series in a current loop, and the current is acquired by acquiring the voltage at two ends of the resistor, so that the current sampling method is realized. A sampling resistor is connected in series with each lower bridge arm of a power device such as an IGBT/MOSFET, and current information of each phase is reproduced through voltage information of the sampling resistor. For a three-phase motor, a common power topology with sampling resistors connected in series in a lower bridge arm is shown in figure 1, the power ground is GND, and three-phase current is reproduced by differentially sampling voltages A-B, C-D, E-F.
A common differential sampling circuit is shown in fig. 2, and a connection manner of the common differential sampling circuit and the lower bridge arm series connection sampling resistor is shown in fig. 3. The sampled current is obtained by differential sampling, biasing and amplifying. When the U-phase current is collected, the reference ground of the bias voltage is a point B; when the phase current of the V-shaped phase is collected, the reference ground of the bias voltage is a point D; when the W-phase current is collected, the reference ground of the bias voltage is point F. When the offset voltage is used to collect the currents of different phases, the reference grounds of the offset voltage are different, and the conventional algorithm always sets the reference voltages of the different phases to the same value, resulting in errors in reproducing the three-phase currents.
Disclosure of Invention
In order to solve the above problems, the present invention provides a three-phase current sampling method for a three-phase motor, which can reproduce three-phase currents of the three-phase motor more accurately.
A three-phase current sampling method of a three-phase motor is characterized in that three-phase output ends of the three-phase motor are respectively connected to connecting points of an upper bridge arm and a lower bridge arm of a three-bridge-arm inverter, the lower bridge arm is respectively connected with a sampling resistor in series and then grounded, and meanwhile, two ends of the three sampling resistors are respectively connected with a differential sampling circuit;
the method comprises the following steps:
s1: the ground end of one of the sampling resistors is arbitrarily selected as a reference ground, the sampling resistor corresponding to the reference ground is defined as Rb, and the phase where the sampling resistor is located is defined as a V phase, the rest two sampling resistors are respectively defined as Ra and Rc, and the phase where the sampling resistor is located is respectively defined as a U phase and a W phase;
s2: obtaining the equivalent resistance R between the sampling resistor Ra and the sampling resistor RbS1Equivalent resistance R between sampling resistance Rc and sampling resistance RbS2；
S3: respectively obtaining equivalent impedances RS1Pressure drop V ofBEquivalent resistance RS2Pressure drop V ofF；
S4: the bias voltage V of the differential sampling circuitBIASAnd a pressure drop VBAs the bias voltage V of the U phaseBIAS-UBias voltage VBIASAnd a pressure drop VFAs the bias voltage V of the W phaseBIAS-W；
S5: obtaining the voltage drop V at two ends of the sampling resistor Ra according to the set function relation satisfied between the bias voltage of each phase and the voltage drop at two ends of the sampling resistorABAnd a voltage drop V across the sampling resistor RcEF；
S6: according to the pressure drop V respectivelyABRatio to sampling resistance Ra, voltage drop VEFThe ratio of the current to the sampling resistor Rc is used to obtain the actual current of the sampling resistor Ra
Sampling the actual current of the resistor Rc
S7: obtaining the actual current of the sampling resistor Rb according to the fact that the sum of the three-phase currents is 0
Therefore, the sampling of the three-phase current of the three-phase motor is realized.
Further, the equivalent resistance R of step S3S1Pressure drop V ofBEquivalent resistance RS2Pressure ofReduce VFThe acquisition method specifically comprises the following steps:
s31: respectively obtaining output voltages V of the differential sampling circuits corresponding to the UOUT-UOutput voltage V of differential sampling circuit corresponding to WOUT-W；
S32: according to the output voltage V respectivelyOUT-UThe ratio of the output voltage to the sampling resistor Ra, and the output voltage VOUT-WThe ratio of the current I to the sampling resistor Rc is obtainedUCurrent I of sampling resistor RcW；
S33: will be equivalent impedance RS1And current IUAs equivalent resistance RS1Pressure drop V ofBEquivalent resistance RS2And current IWAs equivalent resistance RS2Pressure drop V ofF。
Further, the differential sampling circuit comprises an operational amplifier and a resistor R1～R4；
One end of the sampling resistor passes through a series resistor R1Then connected to the positive input terminal of the operational amplifier, and the other end passes through a series resistor R2Then connected to the negative input terminal of the operational amplifier; meanwhile, the positive input end of the operational amplifier passes through a series resistor R3Back-connected to bias supply VBIAS(ii) a Resistance R4Two ends of the operational amplifier are respectively connected with the input negative end and the output end of the operational amplifier;
for the sampling resistor Ra, the set functional relationship between the bias voltage of each phase and the voltage drop across the sampling resistor is specifically as follows:
wherein, VOUT-UIs the output voltage of the differential sampling circuit connected with the two ends of the sampling resistor Ra;
for the sampling resistor Rc, the set functional relationship between the bias voltage of each phase and the voltage drop at two ends of the sampling resistor is specifically as follows:
wherein, VOUT-WIs the output voltage of a differential sampling circuit connected across a sampling resistor Rc.
Has the advantages that:
the invention provides a three-phase current sampling method of a three-phase motor, which takes equivalent impedance introduced by a connecting circuit and the like between sampling resistors into consideration, obtains the actual value of each phase offset voltage according to the voltage drop at two ends of the equivalent impedance, and finally obtains the actual voltage drop at two ends of each sampling circuit according to the actual value of each phase offset voltage, thereby more accurately sampling the three-phase current of the three-phase motor.
Drawings
FIG. 1 is a power topology diagram of a lower bridge arm series sampling resistor of a conventional three-bridge arm inverter;
FIG. 2 is a circuit schematic of a prior art differential sampling circuit;
FIG. 3 is a schematic diagram of a connection mode of a conventional differential sampling circuit and a sampling resistor connected in series with a lower bridge arm;
fig. 4 is a flowchart of a three-phase current sampling method of a three-phase motor according to the present invention;
fig. 5 is a schematic diagram of impedances between sampling circuits provided by the present invention.
Detailed Description
In order to make the technical solutions better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.
Referring to fig. 4, the figure is a flowchart of a three-phase current sampling method of a three-phase motor according to this embodiment. A three-phase current sampling method of a three-phase motor is characterized in that three-phase output ends of the three-phase motor are respectively connected to connecting points of an upper bridge arm and a lower bridge arm of a three-bridge-arm inverter, a sampling resistor is respectively connected to the lower bridge arm in series, two ends of each of three sampling resistors are respectively connected with a differential sampling circuit, and one ends of the three sampling resistors are connected with the same ground.
It should be noted that the connection of the three-phase motor, the three-bridge arm inverter, and the differential sampling circuit may adopt a structure as shown in fig. 3, where, for simplicity, only the differential sampling circuit in which both ends of the sampling resistor Rc of the W-phase lower bridge arm are connected is shown in fig. 3.
The three-phase current sampling method of the present embodiment will be described in detail below by taking the circuit topology shown in fig. 3 as an example. The method comprises the following steps:
s1: and (3) optionally selecting the grounding end of one of the sampling resistors as a reference ground, defining the sampling resistor corresponding to the reference ground as Rb, and defining the phase of the sampling resistor as a V phase, and respectively defining the rest two sampling resistors as Ra and Rc.
It should be noted that, after the ground terminal of one of the sampling resistors is used as the reference ground, the voltage drop between the sampling resistor and the reference ground is 0, that is, the impedance is 0, and since the remaining two sampling resistors have a connection line with a certain length with the reference ground, a certain equivalent impedance exists between the remaining two sampling resistors and the reference ground. That is, the ground terminal of one of the sampling resistors is selected as the reference ground in the embodiment to show the equivalent impedance between the sampling resistors.
S2: obtaining the equivalent resistance R between the sampling resistor Ra and the sampling resistor RbS1Equivalent resistance R between sampling resistance Rc and sampling resistance RbS2And the phases are defined as a U phase and a W phase, respectively.
The equivalent resistance R between the sampling resistor Ra and the sampling resistor RbS1Introduced by the impedance of a connecting line between two sampling resistors and the like, and the equivalent impedance R between the sampling resistor Rc and the sampling resistor RbS2The same reason is also introduced by the impedance of the connecting line between the two; meanwhile, as shown in fig. 5, since there is impedance between B, D, F points and there is a voltage difference between the three points, the bias voltages of different phases are different.
S3: respectively obtaining equivalent impedances RS1Pressure drop V ofBEquivalent resistance RS2Pressure drop V ofF。
Further, the equivalent resistance RS1Pressure drop V ofBAnd etcEffective impedance RS2Pressure drop V ofFThe acquisition method specifically comprises the following steps:
s31: respectively obtaining output voltages V of the differential sampling circuits corresponding to the UOUT-UOutput voltage V of differential sampling circuit corresponding to WOUT-W。
S32: according to the output voltage V respectivelyOUT-UThe ratio of the output voltage to the sampling resistor Ra, and the output voltage VOUT-WThe ratio of the current I to the sampling resistor Rc is obtainedUCurrent I of sampling resistor RcW。
S33: will be equivalent impedance RS1And current IUAs equivalent resistance RS1Pressure drop V ofBEquivalent resistance RS2And current IWAs equivalent resistance RS2Pressure drop V ofF。
S4: the bias voltage V of the differential sampling circuitBIASAnd a pressure drop VBAs the bias voltage V of the U phaseBIAS-UBias voltage VBIASAnd a pressure drop VFAs the bias voltage V of the W phaseBIAS-W。
That is, when the point D is taken as the reference ground, there are:
VD＝0V VBIAS-V＝VBIAS (1)
VB＝IU×RS1 VBIAS-U＝VBIAS+VB (2)
VF＝IW×RS2VBIAS-W＝VBIAS+VF (3)
wherein, IU＝VOUT-U/Ra，IW＝VOUT-W/Rc，VBIASBias voltage, V, for a bias supply of a differential sampling circuitBIAS-VIs a bias voltage corresponding to V, VBIAS-UBias voltage of U phase, VBIAS-WIs the bias voltage of the W phase.
S5: obtaining the voltage according to a set function relation satisfied between each phase bias voltage and the voltage drop at two ends of the sampling resistorVoltage drop V to both ends of sampling resistor RaABAnd a voltage drop V across the sampling resistor RcEF。
It should be noted that the set functional relationship is determined by a circuit structure between a differential sampling circuit and a sampling resistor, that is, when determining which type of differential sampling circuit is selected, the set functional relationship satisfied between the bias voltage of each phase and the voltage drop across the sampling resistor is determined accordingly; meanwhile, the set functional relation is actually a functional relation among the output voltage of the differential sampling circuit, the bias voltage of each phase and the voltage drop at two ends of the sampling resistor; the derivation of one of the expressions of the set functional relationship is given below with respect to the differential sampling circuit shown in fig. 3. As shown in fig. 3, the differential sampling circuit of the present embodiment includes an operational amplifier and a resistor R1～R4；
One end of the sampling resistor passes through a series resistor R1Then connected to the positive input terminal of the operational amplifier, and the other end passes through a series resistor R2Then connected to the negative input terminal of the operational amplifier; meanwhile, the positive input end of the operational amplifier passes through a series resistor R3Back-connected to bias supply VBIAS(ii) a Resistance R4Two ends of the operational amplifier are respectively connected with the input negative end and the output end of the operational amplifier; then there are:
wherein, VOUT-UIs the output voltage of the differential sampling circuit connected with the two ends of the sampling resistor Ra; wherein, VOUT-WThe output voltage of the differential sampling circuit is connected to two ends of the sampling resistor Rc;
the functional relations among the output voltage of the differential sampling circuit, the voltage drop of the equivalent resistor and the voltages at two ends of the sampling resistor corresponding to the sampling resistor Ra can be obtained by the formulas (4) and (5), and the functional relations among the output voltage of the differential sampling circuit, the voltage drop of the equivalent resistor and the voltages at two ends of the sampling resistor corresponding to the sampling resistor Rc are respectively as follows:
further, substituting equations (2) and (3) into equations (6) and (7), respectively, then
It should be noted that, for other differential sampling circuits, according to the specific circuit structure of the differential sampling circuit and the parameters of the adopted components, the functional relation among the output voltage of the differential sampling circuit, the voltage drop of the equivalent resistor, and the voltages at the two ends of the sampling resistor can also be derived in the same manner.
S6: according to the pressure drop V respectivelyABRatio to sampling resistance Ra, voltage drop VEFThe ratio of the current to the sampling resistor Rc is used to obtain the actual current of the sampling resistor Ra
Sampling the actual current of the resistor Rc
S7: according to the sum of the three-phase currents being 0, i.e.
Obtain the actual current of the sampling resistor Rb
Therefore, the sampling of the three-phase current of the three-phase motor is realized.
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it will be understood by those skilled in the art that various changes and modifications may be made herein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (3)
1. A three-phase current sampling method of a three-phase motor is characterized in that three-phase output ends of the three-phase motor are respectively connected to connecting points of an upper bridge arm and a lower bridge arm of a three-bridge-arm inverter, the lower bridge arm is respectively connected with a sampling resistor in series and then grounded, and meanwhile, two ends of each of the three sampling resistors are respectively connected with a differential sampling circuit, and the method comprises the following steps:
s1: the ground end of one of the sampling resistors is arbitrarily selected as a reference ground, the sampling resistor corresponding to the reference ground is defined as Rb, and the phase where the sampling resistor is located is defined as a V phase, the rest two sampling resistors are respectively defined as Ra and Rc, and the phase where the sampling resistor is located is respectively defined as a U phase and a W phase;
s2: obtaining the equivalent resistance R between the sampling resistor Ra and the sampling resistor RbS1Equivalent resistance R between sampling resistance Rc and sampling resistance RbS2；
S3: respectively obtaining equivalent impedances RS1Pressure drop V ofBEquivalent resistance RS2Pressure drop V ofF；
S4: the bias voltage V of the differential sampling circuitBIASAnd a pressure drop VBAs the bias voltage V of the U phaseBIAS-UBias voltage VBIASAnd a pressure drop VFAs the bias voltage V of the W phaseBIAS-W；
S5: according to each phase bias voltage and two ends of sampling resistorThe voltage drop V at two ends of the sampling resistor Ra is obtained by the set function relation satisfied between the voltage dropsABAnd a voltage drop V across the sampling resistor RcEF；
S6: according to the pressure drop V respectivelyABRatio to sampling resistance Ra, voltage drop VEFThe ratio of the current to the sampling resistor Rc is used to obtain the actual current of the sampling resistor Ra
Sampling the actual current of the resistor Rc
S7: obtaining the actual current of the sampling resistor Rb according to the fact that the sum of the three-phase currents is 0
Therefore, the sampling of the three-phase current of the three-phase motor is realized.
2. The method for sampling three-phase current of a three-phase motor according to claim 1, wherein the equivalent resistance R of step S3S1Pressure drop V ofBEquivalent resistance RS2Pressure drop V ofFThe acquisition method specifically comprises the following steps:
s31: respectively obtaining output voltages V of the differential sampling circuits corresponding to the UOUT-UOutput voltage V of differential sampling circuit corresponding to WOUT-W；
S32: according to the output voltage V respectivelyOUT-UThe ratio of the output voltage to the sampling resistor Ra, and the output voltage VOUT-WThe ratio of the current I to the sampling resistor Rc is obtainedUCurrent I of sampling resistor RcW；
S33: will be equivalent impedance RS1And current IUAs equivalent resistance RS1Pressure drop V ofBEquivalent resistance RS2And current IWAs equivalent resistance RS2Pressure drop V ofF。
3. A method of sampling three phase current of a three phase electric motor as claimed in claim 1 wherein said differential sampling circuit comprises an operational amplifier and a resistor R1、R2、R3、R4；
One end of the sampling resistor passes through a series resistor R1Then connected to the positive input terminal of the operational amplifier, and the other end passes through a series resistor R2Then connected to the negative input terminal of the operational amplifier; meanwhile, the positive input end of the operational amplifier passes through a series resistor R3Back-connected to a bias voltage VBIAS(ii) a Resistance R4Two ends of the operational amplifier are respectively connected with the input negative end and the output end of the operational amplifier;
for the sampling resistor Ra, the set functional relationship between the bias voltage of each phase and the voltage drop across the sampling resistor is specifically as follows:
wherein, VOUT-UIs the output voltage of the differential sampling circuit connected with the two ends of the sampling resistor Ra;
for the sampling resistor Rc, the set functional relationship between the bias voltage of each phase and the voltage drop at two ends of the sampling resistor is specifically as follows:
wherein, VOUT-WIs the output voltage of a differential sampling circuit connected across a sampling resistor Rc.
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