CN103715953A - Brushless direct current motor rotor position detecting device and phase changing method - Google Patents

Abstract

The invention discloses a brushless direct current motor rotor position detecting device based on the counter EMF triple frequency harmonic and a phase changing method suitable for the brushless direct current motor rotor position detecting device. The brushless direct current motor rotor position detecting device is composed of a Y-shaped connecting three-phase symmetrical resistance network, a voltage bleeder circuit, a band-pass filtering circuit, a zero passage comparison circuit and an optoelectronic isolation circuit. According to the detecting device, the simulation neutral points are built through the star-shaped three-phase symmetrical resistance network, the counter EMF triple frequency harmonic component is extracted from the simulation neutral points, zero passage signals of the counter EMF triple frequency harmonic component are obtained by comparing the counter EMF triple frequency harmonic component with the grounding end, and a microprocessor calculates the zero passage time of the three-phase counter EMF of a brushless direct current motor according to the two times of zero passage signals of the detecting device and the last action time of a switch tube and controls the phase changing according to the zero passage time. By means of the detecting method, the number of components of the rotor position detecting device can be reduced, and the reliability of detecting can be improved.

Description

Brushless DC motor rotor position detecting device and phase change method

Technical field

The invention belongs to machine field, particularly a kind of brshless DC motor (BLDC) detecting apparatus for rotor position and phase change method.

Background technology

The back-emf of brshless DC motor is trapezoidal wave, and supply current is square wave, and control system is less demanding to rotor-position signal, only needs to obtain several discrete rotor key position signals.Brushless DC motor had both had the advantages such as AC motor structure is simple, reliable, easy to maintenance, possessed again that DC motor operational efficiency is high, the feature of good speed adjustment features, added that cost is lower, applied more and more extensive.

Mainly be there are to two kinds of control modes in brshless DC motor: position sensor is controlled and position-sensor-free technology is controlled.Position sensor control method and control circuit are all fairly simple, and control system cost is low, is widely used.But the existence of position transducer, makes electric motor structure become complicated, and the reliability variation of system cannot be moved under some severe operating modes, has limited to a certain extent further popularization and the use of brushless DC motor.

Use position-sensor-free technology to control brushless DC motor, the various drawbacks that can avoid rotor-position sensor to bring.Early stage back-emf triple-frequency harmonics method is a kind of and Based on Back-EMF Method inhomogeneity method for distinguishing, and this is because early stage triple-frequency harmonics method obtains motor commutation signal by the triple-frequency harmonics integration in back-emf.To waveform signal integration, hardware circuit is complicated, realizes difficulty.

Summary of the invention

The object of the present invention is to provide a kind of reliable and stable, lower-cost brushless DC motor rotor position detecting device and detection method.

Realizing technical solution of the present invention is: a kind of BLDC detecting apparatus for rotor position based on back-emf triple-frequency harmonics, comprise that the Y type connecting successively connects three-phase symmetrical resistor network, voltage branch circuit, bandwidth-limited circuit, zero passage comparison circuit and optical coupling isolation circuit, Y type connects three-phase symmetrical resistor network the motor three phase terminals voltage signal of input is superposeed, obtain simulation neutral point voltage, this voltage is after voltage branch circuit dividing potential drop, be transferred to bandwidth-limited circuit, bandwidth-limited circuit is eliminated the high fdrequency component in simulation neutral point voltage signal, low frequency component and DC component, only retain back-emf triple-frequency harmonics information, bandwidth-limited circuit by back-emf communication to zero passage comparison circuit, zero passage comparison circuit compares this information and earth point voltage, obtains back-emf zero cross signal, and this signal is transferred to optical coupling isolation circuit, optical coupling isolation circuit is isolated the signal of input, and signal is exported to extraneous microprocessor.

A phase change method based on the above-mentioned BLDC detecting apparatus for rotor position based on back-emf triple-frequency harmonics, comprises the following steps:

Step 1, microprocessor catch the zero cross signal of optical coupling isolation circuit output, with last time pull-in time subtract each other do poor, obtain Ti interval time of two zero crossings, obtain after Ti interval time judging that according to commutation last time time T c whether interval time Ti is at [0.5Tc, 1.5Tc] in, if, just with new Ti interval time arriving, replace commutation time T c, if Ti is not in above-mentioned scope, this new Ti value interval time is cast out, the commutation time is continued to use the commutation time T c value of last time, does not upgrade;

Step 2, obtain after commutation time T c, then according to switching tube commutation last time Ta operate time, obtain next commutation Ta+Tc constantly, microprocessor commutation constantly control switch pipe carry out commutation operation.

The present invention compared with prior art, its significant advantage is: (1) is when obtaining simulation neutral point voltage, three phase terminals voltage is directly simply added through three substitutional resistances, saved common filtering link, only after bandwidth-limited circuit in filtering, simplified and simulated obtaining of neutral point voltage.(2) when obtaining triple-frequency harmonics zero cross signal, by back-emf triple-frequency harmonics and reference level comparison, be about to triple-frequency harmonics method and be considered as a type of Based on Back-EMF Method, rather than obtain motor commutation signal by the triple-frequency harmonics integration in back-emf, simplified hardware circuit and implementation.(3) on the basis that back electromotive force checkout gear is simplified, what detect is two time intervals between zero cross signal, according to a front switching tube commutation, constantly calculate rotor-position, at this moment can not consider the filtering phase deviation under friction speed, realize the operation of commutation accurately, realize even running and the speed governing of motor.(4) the present invention proposes a kind of rotor position detecting method, can make brushless DC motor even running.

Below in conjunction with accompanying drawing, the present invention is described in further detail.

Accompanying drawing explanation

The flow chart of the rotor position detecting method of Fig. 1 based on checkout gear of the present invention.

Fig. 2 is RC bandwidth-limited circuit.

Fig. 3 is brushless DC motor rotor position detecting device circuit diagram.

Embodiment

In conjunction with Fig. 3, a kind of brushless DC motor rotor position detecting device based on back-emf triple-frequency harmonics of the present invention, comprise that the Y type connecting successively connects three-phase symmetrical resistor network 1, voltage branch circuit 2, bandwidth-limited circuit 3, zero passage comparison circuit 4 and optical coupling isolation circuit 5, the motor three phase terminals voltage signal that Y type connects 1 pair of input of three-phase symmetrical resistor network superposes, obtain simulation neutral point voltage, this voltage is after voltage branch circuit 2 dividing potential drops, be transferred to bandwidth-limited circuit 3, bandwidth-limited circuit 3 is eliminated the high fdrequency component in simulation neutral point voltage signal, low frequency component and DC component, only retain back-emf triple-frequency harmonics information, bandwidth-limited circuit 3 by back-emf communication to zero passage comparison circuit 4, zero passage comparison circuit 4 compares this information and earth point voltage, obtains back-emf zero cross signal, and this signal is transferred to optical coupling isolation circuit 5, the signal of 5 pairs of inputs of optical coupling isolation circuit is isolated, and signal is exported to extraneous microprocessor.

Y type connects three-phase symmetrical resistor network 1 and comprises the first resistance R 1, the second resistance R ₂with the 3rd resistance R ₃, the first resistance R ₁, the second resistance R ₂with the 3rd resistance R ₃one end connect respectively motor three phase terminals voltage u _a, u _b, u _c, after the other end is jointly connected, as Y type, connect the output of three-phase symmetrical resistor network 1.

Voltage branch circuit 2 comprises the 4th resistance R ₄, the 5th resistance R ₅, the 4th resistance R ₄one end output of being connected three-phase symmetrical resistor network 1 with Y type be connected, the other end and the 5th resistance R ₅be connected, the 5th resistance R ₅other end ground connection, the 4th resistance R ₄with the 5th resistance R ₅joint is as the output of voltage branch circuit 2.

Bandwidth-limited circuit 3 comprises the first capacitor C ₁, the second capacitor C ₂with the 6th resistance R ₆; The first capacitor C ₁one end is connected with the output of front end bleeder circuit 2, other end ground connection, the first capacitor C ₁with the 5th resistance R ₅combine and form the low-pass filter circuit of bandwidth-limited circuit front end; The second capacitor C ₂one end is connected with the output of voltage branch circuit 2, the other end and the 6th resistance R ₆be connected, the 6th resistance R ₆other end ground connection, the second capacitor C ₂with the 6th resistance R ₆joint is as the output of bandwidth-limited circuit 3; The second capacitor C ₂with the 6th resistance R ₆combine and form the high-pass filtering circuit of bandwidth-limited circuit; The first capacitor C ₁with the 5th resistance R ₅the low-pass filter circuit forming forms bandwidth-limited circuit together with above-mentioned high-pass filtering road.

Zero passage comparison circuit 4 comprises the 7th resistance R ₇, the 3rd capacitor C ₃, the first diode D ₁and comparator; The 7th resistance R ₇be connected with the output of bandwidth-limited circuit 3, the other end and the 3rd capacitor C ₃one end is connected, the 3rd capacitor C ₃other end ground connection, the 7th resistance R ₇with the 3rd capacitor C ₃form depth filtering circuit, the 7th resistance R ₇with the 3rd capacitor C ₃joint is as the output of depth filtering circuit and be connected with the positive pole of comparator, the positive pole of device input as a comparison, the negative pole input grounding of comparator, the first diode D ₁the anodal input of anode and comparator be connected, the first diode D ₁negative electrode be connected to VCC1 power supply, the output of comparator is as the output of zero passage comparison circuit 4.

Optical coupling isolation circuit 5 comprises the 8th resistance R ₈, the 9th resistance R ₉with light-coupled isolation device; The 8th resistance R ₈4 outputs of one end and front end zero passage comparison circuit be connected, the other end is connected with the input negative terminal of light-coupled isolation device, and as the input of optical coupling isolator, the input of the anode of light-coupled isolation device is connected with VCC1 power supply, negative terminal output ground connection, anode and the 9th resistance R of light-coupled isolation device ₉one end is connected and as the final output of detecting apparatus for rotor position, the 9th resistance R ₉the other end be connected to VCC2 power supply.

A phase change method for detecting apparatus for rotor position based on above-mentioned brshless DC motor back-emf triple-frequency harmonics, comprises the following steps:

Step 1, microprocessor catch the zero cross signal of optical coupling isolation circuit 5 outputs, with last time pull-in time subtract each other do poor, obtain Ti interval time of two zero crossings, obtain after Ti interval time judging that according to commutation last time time T c whether interval time Ti is at [0.5Tc, 1.5Tc] in, if, just with new Ti interval time arriving, replace commutation time T c, if Ti is not in above-mentioned scope, this new Ti value interval time is cast out, the commutation time is continued to use the commutation time T c value of last time, does not upgrade;

Step 2, obtain after commutation time T c, then according to switching tube commutation last time Ta operate time, obtain next commutation Ta+Tc constantly, microprocessor commutation constantly control switch pipe carry out commutation operation.

Be described in more detail below.

The back-emf of brushless DC motor is trapezoidal wave, it comprises first-harmonic and odd higher harmonic components, by the simple superposition to armature three phase terminals voltage, can obtain simulation neutral point voltage, therefrom extract the third-harmonic component of back-emf, carry out integration, integrated value obtains the commutation moment of power device while being zero.When brushless DC motor neutral point is drawn, can directly obtain harmonic signal by lead-out wire; When neutral point is not drawn, can build simulation neutral point by star three-phase symmetrical resistor network, and therefrom obtain harmonic signal.

A kind of brushless DC motor rotor position detecting device based on back-emf triple-frequency harmonics and corresponding detection method, brushless DC machine position detecting device comprises that Y type connects three-phase symmetrical resistor network, voltage branch circuit, bandwidth-limited circuit, zero passage comparison circuit and photoelectric isolating circuit four parts and forms, the substitutional resistance that described Y type connection three-phase symmetrical resistor network is connected to any by three one end forms, the non-common port of three resistance connects respectively motor three phase terminals voltage, other end common port obtains simulating neutral point voltage, connects the output of three-phase symmetrical resistor network as Y type, voltage branch circuit is comprised of two divider resistances, one end of bleeder circuit is connected three-phase symmetrical resistor network output with Y type is connected, Simulation Center point voltage is introduced to checkout gear, two resistance joints are as the output of bleeder circuit, provide the Simulation Center point voltage of suitable amplitude, the other end ground connection of bleeder circuit, the output of bleeder circuit is linked into the bandwidth-limited circuit of rear end, bandwidth-limited circuit is comprised of a low pass filter and a high pass filter, the low-pass filtering electric capacity of low pass filter in filter circuit and a resistance in front end bleeder circuit form, low-pass filtering electric capacity one end is connected with the output of front end bleeder circuit, the other end is connected with bandwidth-limited circuit earth terminal, low-pass filtering electric capacity and divider resistance combine and form the low-pass filter circuit of bandwidth-limited circuit front end, high-pass filtering circuit is comprised of high-pass filtering electric capacity and high-pass filtering resistance, high-pass filtering electric capacity one end is connected with the out splice going splice place of low-pass filtering electric capacity and front end bleeder circuit, the other end is connected with high-pass filtering resistance, the other end of the high-pass filtering resistance ground connection that is connected with low-pass filtering capacity earth end, export as bandwidth-limited circuit high-pass filtering electric capacity and high-pass filtering resistance joint, the output of bandwidth-limited circuit is inputted as zero passage comparison circuit one end, before signal access comparator, will be first through a depth filtering circuit, the output of low-pass filter circuit is connected with depth filtering resistance one end, the depth filtering resistance other end is connected with depth filtering electric capacity one end, depth filtering electric capacity other end ground connection, depth filtering resistance and depth filtering electric capacity form depth filtering circuit, depth filtering resistance is connected as the output of depth filtering circuit and the positive pole of comparator with depth filtering electric capacity joint, the positive pole of device output as a comparison, the negative pole input grounding of comparator, the anode of diode is connected with anodal input of comparator with the output of depth filtering device, the negative electrode of diode is connected to VCC1 power supply, this diode exerts an influence compared with device mainly for preventing the voltage-contrast of sudden change, guarantee stability and the reliability of circuit, the output of comparator is as the output of zero passage comparison circuit, the output of comparison circuit is inputted as optical coupling isolation circuit Yi road, first the output of comparison circuit will pass through current-limiting resistance, current-limiting resistance one end is connected with the output of front end zero passage comparison circuit, the other end is connected with the input negative terminal of light-coupled isolation device, input as optical coupling isolator, the anode input of light-coupled isolation device is connected with VCC1 power supply, the negative terminal output ground connection of light-coupled isolation device, anode is connected as the final output of detecting apparatus for rotor position with optocoupler output resistance one end, and the other end of optocoupler output resistance is connected to VCC2 power supply.

The final output of detecting apparatus for rotor position is linked into microprocessor interrupt trap port, microprocessor catches the zero cross signal of zero crossing detection device output, with last time pull-in time subtract each other do poor, obtain Ti interval time of two zero crossings, obtain according to commutation last time time T c, judging that whether Ti is at a zone of reasonableness after Ti, if one is reasonably worth, just by the new Ti value arriving, replace commutation time T c; If Ti, not in this zone of reasonableness, casts out this new Ti value, the commutation time is continued to use the Tc value of last time, does not upgrade.Obtain after commutation time T c, then according to last time switching tube commutation operate time, calculate next commutation constantly, then microprocessor control switch pipe carries out commutation operation constantly in commutation.

Below in conjunction with embodiment, further illustrate content of the present invention.

Embodiment

Examples of implementation motor used is the air compressor motor using in DC frequency converting air-conditioner, and its parameter is as follows:

(1) motor types: brushless DC motor (BLDCM);

(2) number of pole-pairs: p=2;

(3) rated speed: n=3600rpm;

(4) rated output power: W=650W;

(5) every phase winding resistance: r=0.9 Ω (20 ℃);

(6) every phase winding inductance: L _σ=3.35mH;

(7) operating frequency: f=20～190Hz;

(8) rotor moment of inertia: J=6.55 * 10 ^-4(Kgm ²);

(9) coefficient of potential Ke=13.2(mV/rpm);

(10) moment coefficient K _t=0.392(Nm/A).

The Y type network input termination motor three phase terminals voltage of brushless DC machine position detecting device, the simulation neutral point voltage obtaining will be simulated neutral point voltage signal through electric resistance partial pressure through bleeder circuit, by the voltage signal acquisition with back electromotive force triple-frequency harmonics information in checkout gear.

Band pass filter in the present invention is for having no chance band pass filter, and it is specifically combined by a RC low pass filter and a RC high pass filter, as shown in Figure 2.Low pass filter forms bleeder circuit with front end resistance simultaneously, according to low-pass filter circuit, lists voltage node equation.

$\frac{U_{\mathrm{in}}\left(s\right)-U_1\left(s\right)}{{\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="HDA0000449581130000012.png"\; state="\{\{state\}\}">R</figure-callout>}}_4}=\frac{U_1\left(s\right)}{R_5}+\frac{U_1\left(s\right)}{1/{\mathrm{sC}}_1}---\left(1\right)$

Arrangement can the transfer function A of circuit ₁(s)

$A_1\left(s\right)=\frac{U_1\left(s\right)}{U_{\mathrm{in}}\left(s\right)}=\frac{R_5}{R_4{R}_5{C}_{1}s+R_4+R_5}---\left(2\right)$

Make s=j ω, function is transformed in complex field and is analyzed from S territory

$A_1\left(\mathrm{j\&omega;}\right)=\frac{U_1\left(\mathrm{j\&omega;}\right)}{U_{\mathrm{in}}\left(\mathrm{j\&omega;}\right)}=\frac{R_5}{{\mathrm{jR}}_4{R}_5{C}_1\mathrm{\&omega;}+R_4+R_5}---\left(5\right)$

By formula (3), can be obtained gain and the phase shift expression formula of above-mentioned filter circuit, suc as formula (4) and formula (5).

$\left|A_1\left(\mathrm{\&omega;}\right)\right|=\frac{R_5}{\sqrt{{(R_4+R_5)}^2+{\left(R_4{R}_5{C}_1\mathrm{\&omega;}\right)}^2}}---\left(4\right)$

${\mathrm{\&phi;}}_1\left(\mathrm{\&omega;}\right)=-\mathrm{arctam}\frac{R_4{R}_5{C}_1\mathrm{\&omega;}}{{\mathrm{<figure-callout\; id="4"\; label="R"\; filenames="HDA0000449581130000012.png"\; state="\{\{state\}\}">R</figure-callout>}}_4+R_5}---\left(5\right)$

Wherein, ω is angular frequency, and ω=2 π f.

From formula (4) and formula (5), along with the signal frequency by filter increases, the gain of signal reduces, and phase shift becomes large.Select suitable component parameters, can make foregoing circuit reach desired technical indicator.

In like manner, can partly analyze high-pass filtering, obtain gain and the phase shift expression formula of corresponding high-pass filtering circuit

$A_2\left(s\right)=\frac{U_{\mathrm{out}}\left(s\right)}{U_1\left(s\right)}=\frac{R_6{C}_{2}s}{R_6{C}_{2}s+1}---\left(6\right)$

$A_2\left(\mathrm{j\&omega;}\right)=\frac{U_{\mathrm{out}}\left(\mathrm{j\&omega;}\right)}{U_1\left(\mathrm{j\&omega;}\right)}=\frac{{\mathrm{jR}}_6{C}_2\mathrm{\&omega;}}{{\mathrm{jR}}_6{C}_2\mathrm{\&omega;}+1}---\left(7\right)$

$\left|A_2\left(\mathrm{\&omega;}\right)\right|=\frac{R_6{C}_2\mathrm{\&omega;}}{\sqrt{1+{\left(R_6{C}_2\mathrm{\&omega;}\right)}^2}}---\left(8\right)$

${\mathrm{\&phi;}}_2\left(\mathrm{\&omega;}\right)=\arctan \frac{1}{R_6{C}_2\mathrm{\&omega;}}---\left(9\right)$

By above analysis, can be found out, in theory this part circuit isolated DC component completely.For high-pass filtering part, require it in isolated DC component, reduce the impact on forward part filter circuit result as far as possible.Low pass and high pass two parts filter circuit are merged, form a band pass filter, as shown in Figure 1.

The passive low-pass filtering link of single order RC increasing in band pass filter rear end, as shown in Figure 3, its effect mainly contains two, one, R ₇for rear class current limliting; Its two, R ₇, C ₃signal is carried out to depth filtering.This grade of circuit should only need except high-frequency interferencing signal, other aspects do not exerted an influence.Its gain and phase shift are suc as formula shown in (10) and formula (11)

$\left|A_3\left(\mathrm{\&omega;}\right)\right|=\frac{1}{\sqrt{1+{\left(R_7{C}_3\mathrm{\&omega;}\right)}^2}}---\left(10\right)$

φ ₃(ω)=-arctan(R ₇C ₃ω) （11）

Band pass filter detection method, when making more than 3 time 3 the doubly several high fdrequency component of this band pass filter in eliminating simulation neutral point voltage, also can eliminate the low frequency component and the DC component that wherein comprise, simulate neutral point voltage after band-pass filter, only retain back-emf triple-frequency harmonics information.

From brshless DC motor operation logic, the back-emf triple-frequency harmonics of motor is alternation, and in this case, reference level is directly chosen earthed voltage, through comparator, relatively can obtain back-emf triple-frequency harmonics zero crossing.

In order to prevent that the voltage-contrast of sudden change from exerting an influence compared with device, guarantee stability and the reliability of circuit, added diode, play voltage clamping.Optocoupler is isolated forceful electric power circuit and control circuit effectively, has strengthened the fail safe of system.

According to above theory analysis, resulting zero cross detection circuit can detect and obtain back-emf triple-frequency harmonics zero crossing, and these zero crossings are back-emf zero cross signals.Back-emf zero cross detection circuit as shown in Figure 3.

The final output of detecting apparatus for rotor position is linked into microprocessor interrupt trap port, microprocessor catches the zero cross signal of zero crossing detection device output, with last time pull-in time subtract each other do poor, obtain Ti interval time of two zero crossings, obtain according to commutation last time time T c, judging that whether Ti is at a zone of reasonableness after Ti, if one is reasonably worth, just by the new Ti value arriving, replace commutation time T c; If Ti, not in this zone of reasonableness, casts out this new Ti value, the commutation time is continued to use the Tc value of last time, does not upgrade.Obtain after commutation Tc fiducial time, calculate next commutation time T s, then according to last time switching tube commutation operate time, calculate next commutation constantly, obtain the particular location of rotor, then microprocessor control switch pipe carries out commutation operation constantly in commutation.Above detection method is first carried out efficiency analysis to the back-emf triple-frequency harmonics zero cross signal obtaining, and prevents that interference signal is as zero cross signal use or the undetected survey of zero cross signal, avoids causing that motor operation is not steady.Experimental results show that this method can effectively improve the stability of motor traveling comfort and system.

Claims (7)

1. a brushless DC motor rotor position detecting device, it is characterized in that, comprise that the Y type connecting successively connects three-phase symmetrical resistor network [1], voltage branch circuit [2], bandwidth-limited circuit [3], zero passage comparison circuit [4] and optical coupling isolation circuit [5], Y type connects three-phase symmetrical resistor network [1] the motor three phase terminals voltage signal of input is superposeed, obtain simulation neutral point voltage, this voltage is after voltage branch circuit [2] dividing potential drop, be transferred to bandwidth-limited circuit [3], bandwidth-limited circuit [3] is eliminated the high fdrequency component in simulation neutral point voltage signal, low frequency component and DC component, only retain back-emf triple-frequency harmonics information, bandwidth-limited circuit [3] by back-emf communication to zero passage comparison circuit [4], zero passage comparison circuit [4] compares this information and earth point voltage, obtains back-emf zero cross signal, and this signal is transferred to optical coupling isolation circuit [5], optical coupling isolation circuit [5] is isolated the signal of input, and signal is exported to extraneous microprocessor.

2. brushless DC motor rotor position detecting device according to claim 1, is characterized in that, Y type connects three-phase symmetrical resistor network [1] and comprises the first resistance [R ₁], the second resistance [R ₂] and the 3rd resistance [R ₃], the first resistance [R ₁], the second resistance [R ₂] and the 3rd resistance [R ₃] one end connect respectively motor three phase terminals voltage u _a, u _b, u _c, after the other end is jointly connected, as Y type, connect the output of three-phase symmetrical resistor network [1].

3. brushless DC motor rotor position detecting device according to claim 1, is characterized in that, voltage branch circuit [2] comprises the 4th resistance [R ₄], the 5th resistance [R ₅], the 4th resistance [R ₄] one end output of being connected three-phase symmetrical resistor network [1] with Y type be connected, the other end and the 5th resistance [R ₅] be connected, the 5th resistance [R ₅] other end ground connection, the 4th resistance [R ₄] and the 5th resistance [R ₅] joint is as the output of voltage branch circuit [2].

4. brushless DC motor rotor position detecting device according to claim 1, is characterized in that, bandwidth-limited circuit [3] comprises the first electric capacity [C ₁], the second electric capacity [C ₂] and the 6th resistance [R ₆]; The first electric capacity [C ₁] one end is connected with the output of front end bleeder circuit [2], other end ground connection, the first electric capacity [C ₁] and the 5th resistance [R ₅] combining forms the low-pass filter circuit of bandwidth-limited circuit front end; The second electric capacity [C ₂] one end is connected with the output of voltage branch circuit [2], the other end and the 6th resistance [R ₆] be connected, the 6th resistance [R ₆] other end ground connection, the second electric capacity [C ₂] and the 6th resistance [R ₆] joint is as the output of bandwidth-limited circuit [3]; The second electric capacity [C ₂] and the 6th resistance [R ₆] combining forms the high-pass filtering circuit of bandwidth-limited circuit; The first electric capacity [C ₁] and the 5th resistance [R ₅] low-pass filter circuit that forms forms bandwidth-limited circuit together with above-mentioned high-pass filtering road.

5. brushless DC motor rotor position detecting device according to claim 1, is characterized in that, zero passage comparison circuit [4] comprises the 7th resistance [R ₇], the 3rd electric capacity [C ₃], the first diode [D ₁] and comparator; The 7th resistance [R ₇] be connected with the output of bandwidth-limited circuit [3], the other end and the 3rd electric capacity [C ₃] one end is connected, the 3rd electric capacity [C ₃] other end ground connection, the 7th resistance [R ₇] and the 3rd electric capacity [C ₃] composition depth filtering circuit, the 7th resistance [R ₇] and the 3rd electric capacity [C ₃] joint is as the output of depth filtering circuit and be connected with the positive pole of comparator, the positive pole of device input as a comparison, the negative pole input grounding of comparator, the first diode [D ₁] the anodal input of anode and comparator be connected, the first diode [D ₁] negative electrode be connected to VCC1 power supply, the output of comparator is as the output of zero passage comparison circuit [4].

6. brushless DC motor rotor position detecting device according to claim 1, is characterized in that, optical coupling isolation circuit [5] comprises the 8th resistance [R ₈], the 9th resistance [R ₉] and light-coupled isolation device; The 8th resistance [R ₈] the output of one end and front end zero passage comparison circuit [4] be connected, the other end is connected with the input negative terminal of light-coupled isolation device, and as the input of optical coupling isolator, the input of the anode of light-coupled isolation device is connected with VCC1 power supply, the negative terminal output ground connection of light-coupled isolation device, anode and the 9th resistance [R ₉] one end is connected and as the final output of detecting apparatus for rotor position, the 9th resistance [R ₉] the other end be connected to VCC2 power supply.

7. the phase change method based on brushless DC motor rotor position detecting device claimed in claim 1, is characterized in that, comprises the following steps:

Step 1, microprocessor catch the zero cross signal of optical coupling isolation circuit [5] output, with last time pull-in time subtract each other do poor, obtain Ti interval time of two zero crossings, obtain after Ti interval time judging that according to commutation last time time T c whether interval time Ti is at [0.5Tc, 1.5Tc] in, if, just with new Ti interval time arriving, replace commutation time T c, if Ti is not in above-mentioned scope, this new Ti value interval time is cast out, the commutation time is continued to use the commutation time T c value of last time, does not upgrade;

Step 2, obtain after commutation time T c, then according to switching tube commutation last time Ta operate time, obtain next commutation Ta+Tc constantly, microprocessor commutation constantly control switch pipe carry out commutation operation.

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