CN100426654C - Precision current sensor used for electric machine control - Google Patents

Abstract

A current transducer used for controlling motor consists of a signal regulation unit including a differential amplifier and a voltage reference unit; a signal transmission unit including a pair of double clamping diodes, a DC power supply VCC, a set of capacity and a pair of resistances; a level shift circuit including a differential amplifier with its feedback resistance being at the same value as its input resistance.

Description

A kind of precision current sensor that is used for Electric Machine Control

One, technical field

The present invention relates to a kind of circuit for controlling motor that is used to simplify, improve the sensor device of motor control switch operating frequency.More particularly, what the present invention relates to is to improve current sensor in analog-to-digital conversion (abbreviating the AD conversion as) signal noise ratio before, makes accuracy of detection not be subjected to the influence of switching frequency., switching frequency can be increased to several times from present 20KHz.

Two, background technology

Relating to the always too busy to get away problem of electric machine control system aspect of performance, promptly how to obtain motor phase current information accurately and timely.Unfortunately, these phase current signals are always generated by high-tension Switching Power Supply.This supply voltage is too high, so that digital control unit can not directly be handled these signals, otherwise can damage circuit.Therefore some special current sensor just is developed, these transducers can be delivered to high voltage place current information in the digital signal processor (abbreviating DSP as) or microcontroller (abbreviating MC as) at low-voltage place, simultaneously the low-voltage dc power supply that high-voltage switch power supply and DSP/MC relied on are kept apart.

The circuit that has developed can typically be divided into several functional blocks, as shown in Figure 1.This figure has only shown the phase in normally heterogeneous, high voltage source is made of Vbus+ and Vbus-, when logical switch element 1 and 2 decided still disconnected by the Electric Machine Control algorithm, but their conductings simultaneously at any time, flows to motor 3 from the electric current of switch element 1 and 2 through shunt resistance 4.

Signal-conditioning unit 7 by one (with switch) unsteady positive supply 5 power supplies is directly linked shunt resistance 4, and measuring unit 8 is measured 7 signal output.Because of measuring unit still at high voltage one Side, can not directly receive 8 output at the motor control unit 10 of LVPS one Side.

For addressing the above problem, introduced signal isolator 9, also claim it to make signal transmitter 9, because in fact it does this two things simultaneously, after signal transmitter 9, can be accepted by digital processing element 10 from the voltage or the data of 9 outputs.The shortcoming of this system is that more complicated and speed are slow, and precision also is subjected to the restriction of speed.

An existing example is exactly the IR2277S/IR2177S chip circuit.Signal measurement is that high voltage one Side in chip carries out, and its output is exactly to represent the action of low-voltage pulse Wide degree of the size of current of the shunt resistance of flowing through modulation (PWM) signal.One of shortcoming of this scheme is exactly that operating frequency is low, is no more than 20KHz, and another shortcoming is the synchronizing signal (Sync) that needs extra external control unit.When the electric current on the shunt resistance changed to new value, this circuit needed two synchronizing cycles that new output is settled out.The time waveform figure that carries out the signal transmission in this way is presented at Fig. 2.

Wherein parameter is:

Vmax: the maximum input voltage before input reaches capacity (approximately+250mV);

Vmin: the minimum input voltage before input reaches capacity (approximately-250mV);

Vin: real input voltage from shunt resistance;

Sync: from the low-voltage synchronizing signal of control unit

The P0:PWM output pulse signal;

Vrh: output is with reference to ceiling voltage;

Vr1: output is with reference to minimum voltage;

OUT: analog output voltage.

The example that another transducer transmits current information is the digital communication of isolating via band, HP7860 for example, and this chip circuit is carried out three tasks, i.e. and signal adjustment, signal measurement and isolation also transmit measurement result.Its basic thought is explained by Fig. 3.Wherein 13 is the modulators (HP7860) that band is isolated, and is used for the voltage of shunt resistance being changed into numerical data and will relying on its own synchronizing signal to send serial data in synchronization (10MHz synchronised clock).Can not be accepted by common digital control unit 17 from the data-signal that HP7860 comes out,, (HPx870) be used as modulating the digital interface between isolator 13 and the digital control unit 17 so a kind of digital interface chip 14 is provided again.Because of each shunt resistance passage all needs such chip 14, total cost has just improved, and complexity has increased in polyphase machine control.

Another shortcoming of HP7860 is that resolution reduces with the message transmission rate raising, for example will transmit 12 accuracy datas, and then Chuan Shu delay is 18uS, postpones when requiring 14 precision to reach 94uS, substantially exceeds general switch periods 50us=1/20Khz.

From above to the introduction of prior art as can be seen, wish to have one from shunt resistance 4 to digital control unit the simpler current detection circuit 10, and can keep accuracy of detection simultaneously improving detected speed signal.

Three, summary of the invention

1, goal of the invention: the purpose of this invention is to provide a kind of precision current sensor that is used for Electric Machine Control that a kind of circuit is simple, detection speed is fast, accuracy of detection is high.

2, technical scheme: a kind of precision current sensor that is used for Electric Machine Control is characterized in that it comprises:

(1) signal adjustment unit, comprising:

A differential amplifier;

A Voltage Reference unit;

(2) signal transmission units, comprising:

A pair of pair of clamping diode;

A DC power supply VCC provides enough voltage, makes when the low-side switch element conductive two clamping diodes that clamping action can take place;

One group of electric capacity comes holding current information;

A pair of resistance come electric capacity is filled or discharges, and restriction flows to the electric current of clamping diode;

(3) level shift circuits comprise:

A differential amplifier, its feedback resistance and input resistance are same values.

Output circuit is wherein linked an analog to digital converter (AD), this AD or independently, or in the DSP/MC sheet.

Input circuit wherein is the shunt resistance as the electric current Sensitive Apparatus of linking each phase of polyphase machine control system, and each needs an independent sort circuit mutually.

Signal adjustment unit before signal transmission unit has comprised a differential amplifier in the signal adjustment unit.

The Voltage Reference unit is provided in the signal adjustment unit, has come the bipolar signal of signal adjustment unit input is become unipolarity output.

Described signal transmission unit, when transmitting current signal, the isolated high voltage district is to the interference of low-voltage area.Wherein contain a pair of identical diode, import from the signal of signal adjustment unit output.Contain a pair of resistance, coming provides bias voltage to the electric capacity of clamping diode and holding current information.Contain one or two or three electric capacity, keep containing the voltage of current information.The voltage of the electric capacity that is recharged outputs to electrical level shift units and goes.The time constant that is formed by electric capacity and resistance is less than the electrical time constant of motor.

Between signal transmission unit and AD analog to digital converter, contain an electrical level shift units.Wherein contain a gain and be one differential amplifier, come non-zero reference voltage that the movable signal delivery unit comes to the reference of analog to digital converter (AD) input.

Design feature of the present invention is: the signal measurement unit in the existing circuit is got rid of, so just simplified circuit, reduced cost, select the AD of various kinds that flexibility is provided to the user.Because present many DSP/MC have miscellaneous to go up analog-to-digital conversion (AD) functional block.

Another characteristics of the present invention are, the signal adjustment unit of a special use is provided, and it can amplify current signal from shunt resistance linearly to be fit to the needs of analog to digital converter (AD) input range.For example be amplified to several volts from the hundreds of millivolt, another critical function is to improve signal noise ratio before signal is sent to low-pressure end.

Another characteristics of the present invention are, introduce a differential amplifier in signal adjustment unit, and its input directly is connected to the two ends of shunt resistance.

Another characteristics of the present invention are, when the analog to digital converter in digitial controller 10 (AD) input range is a unipolarity or only on the occasion of scope, for example 0 to 3 volt, and the current signal that flows through on the shunt resistance is a bipolarity, promptly have just having negative, a Voltage Reference unit is provided in the differential amplifier back, has so just made the intermediate value that is output as the AD converter input range corresponding to the signal adjustment unit during zero current on the shunt resistance.

Another characteristics of the present invention are, a kind of special signal transmission unit is provided, and wherein comprise parts that can be described as two clampers, and this design can be simplified the master-plan of circuit.

Another characteristics of the present invention are, a level shifter is provided after signal transmission unit, and its function is the minimum that the minimum input of non-zero that the conducting saturation voltage drop non-zero owing to switch element causes is moved to the AD input, or zero potential.

Because the characteristic of two clamp circuits, in some period of switch periods, the output of signal transmission unit is to follow the output of signal-conditioning unit, signal adjustment unit output is the and then current signal on the shunt resistance forever then, as long as the sampling instant of suitably selecting AD converter according to the state of power switch component is at this moment in the section, then the precision of this current sensor can not be subjected to the restriction of switching frequency, 20Khz for example, 40Khz, 60Khz ...

3, beneficial effect: current sensor circuit provided by the invention, comprising a signal adjustment unit that is placed on before the signal transmission unit, before importing low-voltage area into, just improves signal signal noise ratio, and make current detecting more accurate; It has also comprised a new signal transmission unit, comes the useful signal that the higher-pressure region has been adjusted is sent into low-voltage circuit, simultaneously isolated high-voltage, so just make current measurement more accurate, with reliable, switching frequency is 20KHz no matter the output accuracy of transducer is maintained thus, or higher fast.

Four, description of drawings

Fig. 1 is the structured flowchart of a certain phase current transducer of the existing polyphase machine control of representative.

Fig. 2 is the existing working waveform figure that is used for the phase current sensor chip-IR2277S/IR2177S of Electric Machine Control.

Fig. 3 is another example of existing current sensor, the structure chart of HP7860 chip.

Fig. 4 is new precision current sensor structured flowchart.

Fig. 5 is shunt resistance/signal adjustment unit structure chart.

Fig. 6 is the schematic diagram that is used for new-type signal transmitter of the present invention.

Fig. 7 is the structure chart of electrical level shift units.

Five, embodiment

The present invention will further set forth with diagram in the following description, and each parts all uses their numbering to represent in the full text in the back among the figure.

Do according to characteristics of the present invention, Fig. 4 is a kind of new precision current sensor system, and this Circuits System comprises 19, one signal transmission units 20 of 4, one signal adjustment units of shunt resistance and an electrical level shift units 21.Originally the signal measurement unit in Fig. 18 is removed in this design, thereby has simplified circuit, has reduced cost, has also eliminated the signal delay that this element causes widely.

Fig. 5 is a kind of realization of signal adjustment unit 19 in the new sensing system (Fig. 4), is characterized in having introduced differential amplifier 24, amplifies the current signal that comes from shunt resistance linearly.

Another characteristics of the present invention are, have only used resistance as feedback and input element in amplifier 24, and input resistance is connected to the shunt resistance current path of motor, can also keep quick response when reducing cost like this, and signal wherein has:

U1H and U2H: the voltage signal at shunt resistance 4 two ends;

V2: the output of amplifier 24;

V1: amplifier output reference point, the top of being linked switch element 2;

(V2-V1): the output of signal adjustment unit 23;

(V2-V1) max: output maximum magnitude.

Another characteristics of the present invention are, a Voltage Reference unit 29 wherein is provided, and come the bipolar signal of signal adjustment unit input is become unipolarity output.Half of the maximum output of signal adjustment unit elected in its output as, that is:

$\frac{{(V_2-V_1)}_{\mathrm{<figure-callout\; id="2"\; label="max"\; filenames="C20061009747000101.png,C20061009747000121.png"\; state="\{\{state\}\}">max</figure-callout>}}}{2}$

The value of two feedback resistances 27,28 all equals Rf among Fig. 5, and the value of two input resistances 25,26 all equals Rin.The input range of supposing analog to digital converter (AD) is (V2-V1) max, then has:

$V_2-{\mathrm{<figure-callout\; id="1"\; label="V"\; filenames="C20061009747000121.png"\; state="\{\{state\}\}">V</figure-callout>}}_1=(U_{2H}-U_{1H})*\frac{R_f}{R_{\mathrm{in}}}+\mathrm{Voltage\; Re\; ference}$

$=(U_{2H}-U_{1H})*\frac{R_f}{R_{\mathrm{in}}}+\frac{{(V_2-V_1)}_{\mathrm{<figure-callout\; id="2"\; label="max"\; filenames="C20061009747000101.png,C20061009747000121.png"\; state="\{\{state\}\}">max</figure-callout>}}}{2}$

The gain here should be elected as:

$\mathrm{Gain}=\frac{R_f}{R_{\mathrm{in}}}=\frac{(V_2-V_1)\mathrm{<figure-callout\; id="2"\; label="max"\; filenames="C20061009747000101.png,C20061009747000121.png"\; state="\{\{state\}\}">max</figure-callout>}}{2*(U_{2H}-U_{1H})\max }$

For example, (U _2h-U _1h) _Max=0.2V, (V ₂-V ₁) _Max=3V, R _In=1.00k then has:

$R_f=R_{\mathrm{in}}*\mathrm{Gain}=R_{\mathrm{in}}*\frac{{(V_2-V_1)}_{\mathrm{<figure-callout\; id="2"\; label="max"\; filenames="C20061009747000101.png,C20061009747000121.png"\; state="\{\{state\}\}">max</figure-callout>}}}{2*{(U_{2h}-U_{1h})}_{\max }}=1.00k*\frac{3.0\mathrm{<figure-callout\; id="2"\; label="V"\; filenames="C20061009747000101.png,C20061009747000121.png"\; state="\{\{state\}\}">V</figure-callout>}}{2*0.2V}=7.5k$

In Fig. 5, may be hundreds of volts or higher between the positive and negative voltage sources Vbus+ of Switching Power Supply and the Vbus-, when switch element 1 and 2 alternately during break-make, the voltage drop on it is also alternately in a switch periods time and a few hectovolt, the time and be saturated to and have only one or two volt.So the output reference point V1 of signal-conditioning unit also fluctuates between all inherent several hectovolts and a few volt, so the digital control unit 10 that signal V1 and V2 can not directly receive in the transducer goes thereupon.

Another characteristics of the present invention are, a kind of special signal transfer circuit is provided, and isolate the signal of the low-voltage area of the high voltage region that contains signal adjustment unit 19 in the new transducer and back, are shown in Fig. 6.

Another characteristics of the present invention are, comprise the diode 33,34 that is called two clampers among Fig. 6, and their parameter is identical, and its negative terminal is received the output V1 of signal adjustment unit 32, V2.If the position of the signal transmission unit 20 in the new transducer (Fig. 4) is placed near positive switching voltage Vbus+ place, then the polarity of two diodes all will connect conversely.

Another characteristics of the present invention are, electric capacity 35,36 is provided in Fig. 6, and 37 come holding current information, also provide resistance 38,39 to come to provide bias voltage to the electric capacity of clamping diode and holding current information.

Another characteristics of the present invention are, the voltage on the electric capacity in the signal transmission unit is output to electrical level shift units and goes, and the power supply VCC of delivery unit must be higher than V1min and V2min more than the three ten-day period of hot season, just:

[(V2-V1)max+V1min]

V1min is the saturation voltage drop of switch element 2.Like this when switch element 2 conductings and 1 when turn-offing, output V1, the V2 of signal adjustment unit 32 also falls to relative Vbus-and have only several volts.The output signal U 1L of signal transmission unit and U2L by diode 33,34 by clamp to V1 and V2.At this moment U2L voltage follow V2, U1L voltage follow V1, the centre only differs from a diode drop.Current information (U2H-U1H) has been sent to the positive terminal of diode like this from shunt resistance 4, i.e. and (U2L-U1L), and remain on the electric capacity.

Yet clear condition is not always so, for example when switch element 1 conducting and during 2 shutoffs, U2L and U1L do not follow V2 and V1.At this moment two clamping diodes are owing to anti-bias voltage blocks, (this moment) high voltage V1, and V2, U1H, U2H almost reach Vbus+, but are isolated by 33,34, and current information (U2L-U1L) then has been left on the electric capacity.

Another characteristics of the present invention are that by resistance 38,39 and electric capacity 35,36, any time constant that forms between 37 is less than the electrical time constant of motor.The clamp that the Electric Machine Control algorithm that has fixes on switch periods to the sampling instant of analog-to-digital conversion (AD) is in the period, and time constant can be littler under such situation, even electric capacity 35,36,37 cancellations.

In other algorithm, for example sampling fixes on switch element 1 conducting and 2 periods of turn-offing, and then electric capacity must keep, and electric capacity will keep (U2L-U1L) long enough, arrives until the AD sampling.

Time constant R1C1 (38,37 combination) and R2C2 (39,36 combination) and the time constant of other combination can determine generally have according to AD sampling algorithm among the DSP/MC:

$\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="C20061009747000121.png"\; state="\{\{state\}\}">R</figure-callout>}1<figure-callout\; id="1"\; label="*\; C"\; filenames="C20061009747000121.png"\; state="\{\{state\}\}">*</figure-callout>C1=\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="C20061009747000101.png,C20061009747000121.png"\; state="\{\{state\}\}">R</figure-callout>}2<figure-callout\; id="2"\; label="*\; C"\; filenames="C20061009747000101.png,C20061009747000121.png"\; state="\{\{state\}\}">*</figure-callout>C2>\frac{T_{\mathrm{hold}}}{5}$

T _HoldBe the period that the voltage (U2L-U1L) on the electric capacity can keep 1% accuracy, AD sampling at this moment section finish to come to.

As needs T _HoldThe time, any two in three electric capacity 35,36,37 just are enough to finish above task.

Have in mind from circuit safety, the reverse withstand voltage of two clamping diodes will be higher than supply voltage switch, and various surges that circuitry processes produces and wink are towards magnitude of voltage.

According to another characteristics of the present invention, provide an electrical level shift units (Fig. 7).When signal U1L followed the output minimum V1min of the signal adjustment unit 32 among Fig. 6, V1min was actually the saturation voltage drop of switch element 2, and just several volts of size are not zero.The input reference point of analog to digital converter (AD) is a fixed value, such as lies prostrate with respect to zero of earth point.Electrical level shift units can move on to any nonzero value reference point of being brought by switch element saturation voltage drop non-zero the reference point of AD converter.

According to another characteristics of the present invention, in electrical level shift units, provide a differential amplifier 42.The value of its all input resistance and feedback resistance is all the same, equals R.So its gain is one, has:

(Vad2-Vad1)＝(U2L-U1L)

According to another characteristics of the present invention, amplifier output reference point Vad1 directly is connected to the input reference point ADC_GND of AD converter.

Claims (7)

1, a kind of precision current sensor that is used for Electric Machine Control, its feature comprises:

(1) signal adjustment unit, comprising:

A differential amplifier;

Behind above-mentioned differential amplifier, be provided with a Voltage Reference unit;

(2) be provided with a signal transmission unit behind above-mentioned signal adjustment unit, this signal transmission unit comprises:

The diode of a pair of pair of clamp, input is from the signal of described signal adjustment unit output;

A DC power supply VCC provides enough voltage, makes when the low-side switch element conductive two clamping diodes that clamping action can take place;

One group of electric capacity comes holding current information;

A pair of resistance, coming provides bias voltage to the electric capacity of two clamping diodes and described holding current information, and to the electric capacity charge or discharge, and restriction flows to the electric current of two clamping diodes;

(3) be provided with a level shift circuit behind above-mentioned signal transmission unit, this level shift circuit comprises:

Another differential amplifier, the reference that the non-zero reference voltage that comes the movable signal delivery unit is imported to analog to digital converter, its feedback resistance and input resistance are same values.

2, precision current sensor according to claim 1 is characterized in that the output of level shift circuit is connected to an analog to digital converter, this analog to digital converter or independently, or in the DSP/MC sheet.

3, precision current sensor according to claim 1, the input circuit that it is characterized in that signal adjustment unit is the shunt resistance as the electric current Sensitive Apparatus that is connected to each phase of polyphase machine control system, and each needs the input circuit of an independent sort signal adjustment unit mutually.

4, precision current sensor according to claim 1 is characterized in that described signal transmission unit, and when transmitting current signal, the isolated high voltage district is to the interference of low-voltage area.

5, precision current sensor according to claim 4 is characterized in that described signal transmission unit contains one or two or three electric capacity, keeps containing the voltage of current information.

6, precision current sensor according to claim 4 is characterized in that the voltage of the electric capacity that is recharged outputs to level shift circuit.

7, precision current sensor according to claim 4 is characterized in that the time constant that formed by electric capacity in the described signal transmission unit and the resistance electrical time constant less than motor.

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