CN1100811A - Method for measuring pulse width modulated power for dc motor and converting device - Google Patents

Abstract

The method uses a coupler to measure the voltage pulse signal and current signal of a PWM modulated DC servo motor in real time and uses the current signal to modulate the voltage pulse signal through a pulse width modulating circuit, thus the width of modulated pulse signal will be proportional to the power of the motor, it combines analog electronic technique and digital control logic into anintegrity, and it features simple structure, high conversion precision and high reliability.

Description

Method for measuring pulse width modulated power for dc motor and converting device

The present invention relates to new method and conversion equipment that a kind of motor power (output) detects, especially be applicable to the power detection of the DC servo-motor of PWM modulation.

At present, the detection principle of disclosed electric power mainly contains two kinds: (1) carries out the computing evaluation with the analog quantity process Hall element of electric current and voltage or the analog multiplier of integrated circuit, output and the voltage analog signal that is directly proportional of detected power are as 2885 power converters of Japanese Yokogawa Co., Ltd. production; (2) through analog to digital converter the voltage and current signal is sampled, pass through the digital operation evaluation again.As (publication number: CN1067744A) exactly voltage, electric current and environment temperature are sampled and analog to digital conversion, utilize Fourier analysis method to calculate performance number in the unit by microprocessor then in Chinese invention patent communique on January 6th, 1 disclosed " measuring the method and the device of electric power and electric energy ".But when measuring the power of PWM modulation DC servo-motor, the measurement mechanism output based on principle (1) is actually the linear modulation of current signal to the voltage pulse signal amplitude, and output signal must just can obtain practical power signal through filtering.Because all there is nonlinearity erron inevitably in analog multiplier, and has also filtered many useful multidate informations in filtering, therefore, when detecting the power of DC servo-motor of PWM modulation based on principle (1), measurement mechanism complexity not only, the cost height, and also precision is low.On the other hand, because the voltage signal of PWM modulation is a high-frequency pulse signal, existing power detection device based on principle (2), because sample frequency is restricted, the power signal error of measuring is very big in real time.

The objective of the invention is to, overcome above-mentioned the deficiencies in the prior art, a kind of simply and effectively detection method is provided, its ultimate principle is as follows:

(1) measure the voltage V(t of motor in real time with linear coupling isolator) and current i (t), motor voltage signal V obtained _i(t) and motor current signal i _i(t).

DC servo-motor for the PWM modulation has:

h, nT ≤t ≤nT + t _V

V(t)=｛ (1)

0, nT + t _v＜t ＜(n + 1) T

In the formula, the T-motor voltage opens and closes the cycle;

t _v-one voltage opens and closes interior closure time of cycle;

The h-constant.

Be the voltage V(t of motor) be the series of rectangular potential pulse, its amplitude is h, pulse width is that a voltage opens and closes the closure time t in the cycle _v

The coupling back:

1 ₁*h, nT ≤t ≤nT + t _v

v ₁(t) = 1 ₁*V(t) = ｛ (2)

0, nT + t _v＜t ＜(n + 1)T

i _i（t）＝l ₂＊i（t） （3）

In the formula, l ₁, l ₂-be constant;

(2) motor current signal i _i(t) linear transformation becomes a voltage signal V _Ii(t)

V _ii（t）＝l ₃＊i _i（t）＝l ₂＊l ₃＊i（t） （4）

Wherein, l ₃-constant.

(3) at nT≤t≤nT+t _VDuring this time, to V _Ii(t) carry out integration, obtain voltage signal V _a(t).When integration finishes, V _a(t) reach maximal value V _Amax

${\mathrm{\&mu;}}_e=\frac{1}{\frac{1}{\mathrm{\&mu;}}+N_d}<5>$

$={\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="93112171X\_DRIMG1.png,93112171X\_DRIMG2.png"\; state="\{\{state\}\}">l</figure-callout>}}_2*{\mathrm{<figure-callout\; id="3"\; label="l"\; filenames="93112171X\_DRIMG1.png,93112171X\_DRIMG2.png"\; state="\{\{state\}\}">l</figure-callout>}}_3*{\mathrm{<figure-callout\; id="4"\; label="l"\; filenames="93112171X\_DRIMG1.png"\; state="\{\{state\}\}">l</figure-callout>}}_4{\&Integral;}_{\mathrm{nT}}^{\mathrm{nT}+t_v}i\left(t\right)\mathrm{dt}---\left(5\right)$

Wherein, l ₂, l ₃, l ₄-be constant.

(4) as t＞nT+t _VThe time, make V _a(t) at the uniform velocity reduce; Work as t=nT+t _V+ t _PnThe time, V _a(t)=0.After this, V _a(t) keep 0, until again to V _Ii(t) integration.

dV _a（t）/dt＝-l ₅，nT+t _V＜t≤nT+t _V+t _pn（6）

V _amax＝l ₅＊t _pn（7）

$t_{\mathrm{pn}}=V_{a\max }/{\mathrm{<figure-callout\; id="5"\; label="l"\; filenames="93112171X\_DRIMG2.png"\; state="\{\{state\}\}">l</figure-callout>}}_5=({\mathrm{<figure-callout\; id="2"\; label="l"\; filenames="93112171X\_DRIMG1.png,93112171X\_DRIMG2.png"\; state="\{\{state\}\}">l</figure-callout>}}_2*{\mathrm{<figure-callout\; id="3"\; label="l"\; filenames="93112171X\_DRIMG1.png,93112171X\_DRIMG2.png"\; state="\{\{state\}\}">l</figure-callout>}}_3*{\mathrm{<figure-callout\; id="4"\; label="l"\; filenames="93112171X\_DRIMG1.png"\; state="\{\{state\}\}">l</figure-callout>}}_4/l_5)*{\&Integral;}_{\mathrm{nT}}^{\mathrm{nT}+t_v}i\left(t\right)\mathrm{dt}---\left(8\right)$

Wherein, l ₅-constant;

t _Pn-V _a(t) from t=nT+t _VConstantly by V _a(t)=V _AmaxBe decreased to V _a(t)=0 time.

(5) at time nT+t _V＜t＜nT+t _V+ t _PnRectangular pulse signal of interior formation, pulse width is t _Pn, t _PnOpen and close average power P cycle at nT to voltage of (n+1) T with motor _n(being cell power) is directly proportional.

$P_n=l/T*{\&Integral;}_{\mathrm{nT}}^{(n+1)T}i\left(t\right)*V\left(t\right)\mathrm{dt}$

$P_n=l/T*{\&Integral;}_{\mathrm{nT}}^{(n+1)T}i\left(t\right)*V\left(t\right)\mathrm{dt}$

$=h/T*{\&Integral;}_{\mathrm{nT}}^{\mathrm{nT}+t_v}i\left(t\right)\mathrm{dt}$

= h*l ₅/ (T*l ₂*l ₃*l ₄)*t _pn

= L*t _pn

Wherein, L=h*l ₅/ (T*l ₂* l ₃* l ₄)-constant.

Note the width t of positive rectangular pulse signal _Pn, promptly detect P _n

(6) repeat above-mentioned (3), (4), (5), obtain positive rectangular wave pulse, the positive rectangular pulse signal width of wherein each t _PnWith corresponding P _nBe directly proportional, measure t in real time _PnCan realize P _nReal-time detection.

The pulse width modulated power conversion device of DC servo-motor that the above-mentioned ultimate principle of foundation forms as shown in drawings.This device is by a voltage coupling mechanism 1, and current transducer 2 and pulse width modulation circuit 3 are formed, and it is by voltage coupling mechanism 1 and current transducer 2 input motor voltage V(t) and current i (t), output pulse-width-modulating signal V _o(t).Wherein voltage coupling mechanism 1 is by divider resistance R ₁, R ₂, photoelectrical coupler GD and resistance R ₃Form; Current transducer 2 is by LEM current sensor 4 and outer meeting resistance R ₄Form.Pulse width modulation circuit 3 comprises by operational amplifier A ₁, A ₂And resistance R ₅, R ₆, R ₇The voltage follow-up amplifier of forming is by operational amplifier A ₃And resistance R ₈, the integrating circuit formed of integrating capacitor C; By stabilized voltage supply E, resistance R ₉And operational amplifier A ₃, the reverse integral circuit formed of integrating capacitor C; By voltage comparator A ₅The reference comparator circuit of forming; By voltage comparator A ₄The comparator circuit of forming, and integrated electronic analog switch K ₁, K ₂, K ₃And logic control circuit.The input end of voltage follow-up amplifier links to each other with the output terminal of current transducer 2, input motor current signal i _i(t), its output voltage V _Ii(t) by electronic switch K ₁Receive the input end of integrating circuit.Electronic switch K ₂Be positioned at the resistance R of reverse integral circuit ₉And between the integrating capacitor C, the output voltage of integrating capacitor C

With comparer A ₅Positive input link to each other comparer A ₅Output reference voltage signal V _SO, simultaneously, V _aBy electronic switch K ₃With comparer A ₄Positive input link to each other comparer A ₄Output square voltage pulse signal V _o, V _oBe the output signal of pulse width modulation circuit.Electronic switch K ₁Logic control circuit by V _iBe input to the J-K flip flop B that rising edge triggers ₁Cp end, V _oBy a not gate and trigger B ₁R _aConnect V _oPass through again and door and trigger B by a not gate and a high level ₁J end link to each other trigger B ₁K end put low level and form.Electronic switch K ₂, K ₃Logic control circuit identical, be by V _iBe input to the J-K flip flop B that negative edge triggers ₂Cp end, V _AoWith trigger B ₂R _aEnd links to each other, V _AoWith a high level through one with the door with trigger B ₂J end link to each other trigger B ₂K termination low level form.During trigger output high level, control corresponding electronic switch closes; During the trigger output low level, control corresponding electronic switch and disconnect.

Accompanying drawing 1, be the electrical block diagram of conversion equipment

Accompanying drawing 2, be the circuit diagram of voltage coupling mechanism

Accompanying drawing 3, be the circuit diagram of current transducer

Accompanying drawing 4, be pulse width modulation circuit figure

Accompanying drawing 5, be electronic switch K ₁Logic control circuit figure

Accompanying drawing 6, be electronic switch K ₂, K ₃Logic control circuit figure

Accompanying drawing 7, be conversion equipment work schedule oscillogram

Accompanying drawing 8, be conversion equipment output pulse signal V _o(t) to motor voltage signal V _i(t) the work schedule oscillogram of automatic frequency division

Below in conjunction with a description of drawings most preferred embodiment of the present invention and the course of work.

When circuit is started working, V _oBe low level, trigger B ₁R _aEnd and J end are all put high level; V _AoBe low level, trigger B ₂R _aEnd is put low level, electronic switch K ₂, K ₃Disconnect.At V _iBecome the rising edge of high level, trigger B by low level ₁The output high level, electronic switch K ₁Closure, integrating circuit work, V subsequently _AoBe converted to high level, trigger B ₂R _aEnd and J end are all put high level, but K ₁, K ₂Still keep disconnection.At V _iBecome low level negative edge by high level, trigger B ₂The output high level, electronic switch K ₂, K ₃Closure, reverse integral circuit and comparator circuit work, V _oThe output high level.At V _oThe moment of output high level, trigger B ₁R _aEnd is put low level, trigger B ₁Output low level, electronic switch K ₁Disconnect, integrating circuit quits work, integral voltage

Reach maximal value V _Amax, when the reverse integral circuit makes V _aWhen evenly dropping to zero, V _o, V _AoBecome low level, V _oForm a complete rectangular pulse signal, pulse width is V _aBy V _AmaxT discharge time of integrating capacitor C when evenly dropping to zero _PnSimultaneously, because V _AoBe low level, put trigger B ₂R _aEnd is low level, trigger B ₂Output low level, electronic switch K ₂, K ₃Disconnect, the reverse integral circuit quits work, and V _oFor low level makes trigger B ₁R _aEnd and J end are put high level, but K switch at this moment ₁Still keep disconnection.At V _iWhen becoming the rising edge of high level by low level once more, trigger B ₁Export high level once more, electronic switch K ₁Closure repeats above-described integration and reverse integral process, V again _oForm a rectangular pulse signal once more.Said process has promptly been realized motor current signal i repeatedly _i(t) to electric electromechanics pressure pulse signal V _i(t) pulse-length modulation, the pulse width t of modulation back output _PnWith the average power P of corresponding motor in a voltage switching cycle _nBe directly proportional.

Resistance R in this device ₅And resistance R ₉Adopted variable resistor.Variable resistor R wherein ₅Be used for adjusting to motor current signal i _i(t) amplification coefficient l ₃, variable resistor R ₉Be used to adjust the discharge coefficient l of reverse integral circuit ₅

Open and close the closure time t in cycle at voltage of motor _VLonger, and the current signal i of motor _i(t) V that after amplifying, obtains _IiWhen (t) also big, the pulse-width-modulating signal V of this device output _oCan be automatically to electric electromechanics pressure pulse signal V _i(t) frequency division, but the pulse signal width t of assurance output _PnStill with the power P that detects _nBe directly proportional, its work schedule waveform as shown in Figure 8.

Because the mode that this method and conversion equipment thereof have adopted Analog Electronics Technique and Digital Logic control to combine, have simple in structure, conversion accuracy is high and advantage such as good reliability.

Claims (9)

1, the method for measuring pulse width modulated power of direct current motor is that a kind of DC servo-motor power linear transformation the PWM modulation is the new method of pulse width, it is characterized in that:

1.1 with coupling mechanism the voltage and current of the DC servo-motor of PWM modulation is carried out linearity coupling and isolation, the voltage and current signal after the coupling is directly proportional with the voltage and current of motor respectively, but has isolated electrical communication each other;

1.2 current signal is carried out linear transformation;

1.3 when the motor voltage signal was high level by low transition, the integrating circuit conducting was carried out integration to current signal, obtained an integral voltage; When the motor voltage signal was converted to low level by high level, integrating circuit disconnected, and to the integration termination of current signal, integral voltage reaches maximal value;

1.4 when the motor voltage signal is converted to low level by high level, the reverse integral circuit turn-on, integral voltage at the uniform velocity descends; When integral voltage returned to zero, the reverse integral circuit disconnected, and reverse integral stops;

1.5 the reverse integral process is converted to a rectangular pulse signal, and the width of this rectangular pulse signal equals the reverse integral time, and is directly proportional with the average power of motor in a voltage switching cycle;

1.6 after the reverse integral process stops, repeating integration and reverse integral process next time, obtain another voltage and open and close the rectangular pulse signal that pulse width is directly proportional with the average power of motor in the cycle;

1.7 measure the rectangular pulse signal width of output, obtain power of electric motor.

2, a kind of pulse width modulated power conversion device of direct current motor that forms according to the described method of claim 1., it is made up of voltage coupling mechanism 1 and current transducer 2 and pulse width modulation circuit 3, the input end that it is characterized in that voltage coupling mechanism 1 and current transducer 2 is connected with motor, its output terminal is connected with pulse width modulation circuit 3, pulse width modulation circuit 3 output pulse-width-modulating signals.

3,, it is characterized in that voltage coupling mechanism 1 is by divider resistance R according to the described power conversion device of claim 2. ₁, R ₂, photoelectrical coupler GD and resistance R ₃Form.

4,, it is characterized in that current transducer 2 is by LEM current sensor 4 and external circuits R according to the described power conversion device of claim 2. ₄Form.

5,, it is characterized in that pulse width modulation circuit 3 is by voltage follow amplifying circuit, integrating circuit, reverse integral circuit, form with reference to comparator circuit, comparator circuit, electronic switch and logic control circuit according to the described power conversion device of claim 2..

6,, it is characterized in that the voltage follow amplifying circuit is by operational amplifier A according to the described power conversion device of claim 5. ₁, A ₂And resistance R ₅, R ₆, R ₇Form, its input end links to each other with the output terminal of LEM current sensor 4, and its output terminal is by an electronic switch K ₁Be connected with the input end of integrating circuit; Integrating circuit is by operational amplifier A ₃And resistance R ₃, capacitor C is formed, and the output of integrating circuit links to each other with positive input with reference to comparator circuit, and passes through electronic switch K ₃Be connected with the positive input of comparator circuit; Reverse integral electric routing stabilization pressuring power E, resistance R ₉, electronic switch K ₂And operational amplifier A ₃Form with capacitor C; With reference to comparator circuit by voltage comparator A ₅Form output reference voltage signal V _SO; Comparator circuit is by voltage comparator A ₄Form output pulse-width-modulating signal V _O, its pulse width and the motor power (output) of surveying are directly proportional.

7,, it is characterized in that described logic control circuit is by integral restrictor K according to the described power conversion device of claim 5. ₁Logic control circuit and reverse integral K switch ₂, the comparator circuit K switch ₃Logic control circuit form.

8,, it is characterized in that described integral restrictor K according to the described power conversion device of claim 7. ₁Logic control circuit be output signal V by the voltage coupling mechanism ₁J-K flip flop B with the rising edge triggering ₁Cp end link to each other comparer A ₄Output signal V _oThrough a not gate and J-K flip flop B ₁R _aEnd links to each other, V _OThrough a not gate again with a high level through one with the door output and trigger B ₁J end link to each other, the K end is put low level.

9,, it is characterized in that described reverse integral K switch according to the described power conversion device of claim 7. ₂, the comparator circuit K switch ₃Logic control circuit be output signal V by the voltage coupling mechanism _iJ-K flip flop B with the negative edge triggering ₂Cp end link to each other comparer A ₅The reference voltage signal V of output _SOWith trigger B ₂R _aEnd links to each other, V _SOWith a high level through one with the door with trigger B ₂J end link to each other, the K end is put low level.

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