CN104734581A - Driving method for position-sensorless of permanent magnet brushless direct current motor - Google Patents

Abstract

The invention discloses a driving method for a position-sensorless of a permanent magnet brushless direct current motor, is applied to the permanent magnet brushless direct current motor under a high-speed and heavy-load condition, and belongs to the field of permanent magnet brushless direct current motor controlling. By utilizing the characteristic that the current slop of a follow current phase is a monotone function, by setting a corresponding threshold value, the counter potential of the follow current phase can still be detected when zero crossing point is submerged. The driving method for the position-sensorless of the permanent magnet brushless direct current motor is matched with a traditional counter potential zero crossing point method, the application range of sensorless technology of the permanent magnet brushless direct current motor can be enlarged. A central point of a coil does not need to be connected out, the requirement for the counter potential waveform of the motor is low, and the adaptability is high.

Description

A kind of driving method of permanent-magnet brushless DC electric machine position-sensor-free

Technical field

The invention belongs to the technical field of control method for brushless direct current motor, relate to brushless direct current motor sensorless technology, particularly relate to a kind of driving method of permanent-magnet brushless DC electric machine position-sensor-free.

Background technology

Permanent-magnet brushless DC electric machine (being called for short BLDC motor) control method is simple, and power density is large, and efficiency is high, is widely used in high-speed power and drags occasion.Position-sensor-free technology is as an important research direction of BLDC motor, and eliminate the position transducer of motor, motor axial length is reduced, and decreases the constraints of design of electrical motor, and improves the reliability of system.

Judge that rotor-position is one of BLDC electric machine without position sensor scheme be most widely used based on back-emf zero crossing.

The method is mainly divided into two class research directions: 1) terminal voltage/phase voltage method; 2) triple-frequency harmonics method.

Terminal voltage/phase voltage method detects terminal voltage or the phase voltage of each phase winding, itself and reference signal is compared the zero crossing obtaining back-emf, generates BLDC motor commutation signal after phase shift.But when BLDC motor operates in high-speed overload occasion, winding current rises, the commutation cycle shortens, and phase current not easily afterflow, to zero, causes zero crossing to be submerged, position probing failure.

Triple-frequency harmonics method detects the voltage of winding central point and resistor network mid point.This voltage is equal with the third-harmonic component of opposite potential in theory, and not by the impact of winding afterflow situation, has the higher scope of application.But the method requires that the opposite potential of motor contains larger triple-frequency harmonics, and the central point of winding need be drawn, not only the Electromagnetic Design of motor requires high, is also unfavorable for the machining of motor.

Therefore, in order to expand the operation interval of BLDC electric machine without position sensor algorithm, improve system reliability, under research one overcomes high-speed overload situation, zero crossing floods, and does not have the driving method of the BLDC electric machine without position sensor of particular/special requirement to have greater significance to back-emf and winding connection.

Summary of the invention

Technical problem to be solved by this invention is for defect involved in background technology, a kind of driving method of permanent-magnet brushless DC electric machine position-sensor-free is provided, realize permanent-magnet brushless DC electric machine (BLDC motor) high-speed overload, indirect rotor-position detection when back-emf zero crossing floods, by judging the timely handoff algorithms of winding afterflow situation, extend applicable rotating speed and the load of position-sensor-free algorithm.

The present invention is for solving the problems of the technologies described above by the following technical solutions:

A driving method for permanent-magnet brushless DC electric machine position-sensor-free, comprises the following steps:

Step 1), when the commutation moment arrives, the electric current of Real-time Collection afterflow phase;

Step 2), the afterflow phase current according to collecting solves its current slope;

Step 3), calculate current slope threshold values corresponding to the afterflow phase current that collects according to the busbar voltage of three phase inverter bridge, the equivalent resistance of phase winding, the equivalent d-axis inductometer of phase winding;

Step 4), by step 2) in the current slope that calculates and step 3) in the current slope threshold values that calculates compare;

Step 4.1), when afterflow phase current does not drop to zero, current slope is equal with current slope threshold values, then export position detection signal during afterflow opposite potential zero crossing;

Step 4.2), if current slope is inequal with current slope threshold values yet when the electric current of afterflow phase drops to zero, adopt traditional zero-crossing method to detect, export position detection signal during back-emf zero crossing;

Step 5), position detection signal is carried out phase shift process, generates the drive singal of three phase inverter bridge;

Step 6), the drive singal drive motors according to three-phase inverter runs.

As the further prioritization scheme of driving method of a kind of permanent-magnet brushless DC electric machine of the present invention position-sensor-free, described step 3) in calculate the formula of current slope threshold values corresponding to the afterflow phase current that collects as follows:

${\frac{{\mathrm{di}}_k}{\mathrm{dt}}|}_{e_k=0}=\frac{U_{\mathrm{DC}}-3{\mathrm{Ri}}_k}{3L}\≈\frac{U_{\mathrm{DC}}}{3L}$

In formula, k represents the afterflow phase in ABC three-phase, e _kfor the back-emf of afterflow phase, i _kfor afterflow phase current, U _dCfor the busbar voltage of inverter bridge, L is the equivalent d-axis inductance of brshless DC motor, and R is the phase resistance of brshless DC motor.

The present invention adopts above technical scheme compared with prior art, has following technique effect:

1. when not changing the body construction of BLDC motor, under solving high-speed overload situation, zero crossing floods, the problem that rotor-position cannot detect;

2. effectively supplement the range of application of position-sensor-free algorithm, and there is stronger versatility.

Accompanying drawing explanation

Fig. 1 is the system block diagram of position-sensor-free algorithm of the present invention;

Fig. 2 be A+B-commutation to A+C-, and schematic equivalent circuit when afterflow phase current is not equal to zero;

Fig. 3 (a) is the phase current (i of B phase winding when zero crossing does not flood _b) and phase voltage (U _bn) schematic diagram;

Fig. 3 (b) is the phase current (i of B phase winding when zero crossing floods _b) and phase voltage (U _bn) schematic diagram;

Fig. 4 is BLDC motor ABC tri-opposite potential schematic diagram;

Fig. 5 is the schematic block diagram of current slope threshold values comparison algorithm of the present invention;

Fig. 6 is the schematic block diagram that slope threshold values calculates;

The algorithm waveform schematic diagram that Fig. 7 (a) and Fig. 7 (b) are respectively BLDC motor opposite potential when being difformity;

Fig. 8 is the algorithm flow chart of the present invention when combining with traditional zero-crossing method.

Embodiment

The present invention by the electric current in real-time sampling afterflow mutually, and to compare with related threshold after calculating phase current slope thus indirect detection goes out motor rotor position signal.The method is submerged situation for back-emf zero crossing, provides a kind of driving method of new position-sensor-free, not only lower to the opposite potential waveform requirements of BLDC motor, also without the need to changing electric machine structure.

Below in conjunction with accompanying drawing, technical scheme of the present invention is described in further detail:

The invention discloses a kind of driving method of permanent-magnet brushless DC electric machine position-sensor-free, comprise the following steps:

Step 1), when the commutation moment arrives, the electric current of Real-time Collection afterflow phase;

Step 2), the afterflow phase current according to collecting solves its current slope;

Step 3), calculate current slope threshold values corresponding to the afterflow phase current that collects according to the busbar voltage of three phase inverter bridge, the equivalent resistance of phase winding, the equivalent d-axis inductometer of phase winding;

Step 4), by step 2) in the current slope that calculates and step 3) in the current slope threshold values that calculates compare;

Step 4.1), when afterflow phase current does not drop to zero, current slope is equal with current slope threshold values, then export position detection signal during afterflow opposite potential zero crossing;

Step 4.2), if current slope is inequal with current slope threshold values yet when the electric current of afterflow phase drops to zero, adopt traditional zero-crossing method to detect, export position detection signal during back-emf zero crossing;

Step 5), position detection signal is carried out phase shift process, generates the drive singal of three phase inverter bridge;

Step 6), the drive singal drive motors according to three-phase inverter runs.

BLDC motor driven systems of the present invention is adopted to form as shown in Figure 1, mainly comprise four parts: BLDC motor body, three phase inverter bridge, the control module being core with DSP or other similar chip, and be applicable to back-emf zero crossing and flood the position detecting module with the situation of not flooding (it is interval that zero crossing is positioned at afterflow and non-afterflow).

Wherein, the three-phase current collected is carried out differential by the position detecting module that afterflow opposite potential zero crossing floods, obtain the slope value of three-phase current, when afterflow phase current does not drop to zero, the absolute value of the afterflow phase current slope calculated and threshold values are compared the back-emf zero crossing indirectly obtaining this phase, i.e. rotor-position signal.By this position signalling by the process such as controller phase shift, sector judgement, the drive singal exported can make BLDC motor continue when position-sensor-free to run.

Figure 2 shows that A+B-commutation is to A+C-, and circuit diagram when afterflow phase current is non-vanishing.In figure, n point is the central point of winding, and L is the equivalent d-axis inductance of brshless DC motor, and R is the phase resistance of brshless DC motor, e _a, e _b, e _cfor the back-emf of ABC three-phase.Before commutation, switch transistor T 1, T4 conducting, electric current is by A phase flow direction B phase; During commutation, T4 turns off, and T6 is open-minded, and due to the existence of phase inductance, B phase current cannot be dropped rapidly to zero, thus flows into bus by diode D3 afterflow.Now the terminal voltage value clamper of B phase winding is bus voltage value, and B phase current values reduces, and C phase current values rises.

When BLDC machine operation is at the slow-speed of revolution, little loading condition, afterflow phase current is little and commutating period is long, and before this opposite potential zero crossing arrives, current value drops to zero, and now the phase voltage of winding is this opposite potential.Therefore, the zero crossing of back-emf can be detected by detecting phase voltage, as shown in Fig. 3 (a).

When BLDC machine operation in high rotating speed, heavy load, winding current is large and commutating period is short.After commutation starts, when the back-emf zero crossing of this phase arrives, the electric current of afterflow phase drops to zero not yet.During this period of time, the terminal voltage value of afterflow phase is clamped at all the time as bus voltage value, causes the back-emf zero crossing of this phase cannot be detected, as shown in Fig. 3 (b).

Analyze equivalent electric circuit during fly-wheel diode conducting, ignore switching tube and diode drop, A, B, C three-phase has following voltage equation:

$U_{\mathrm{an}}={\mathrm{Ri}}_a+L\frac{{\mathrm{di}}_a}{\mathrm{dt}}+e_a---\left(1\right)$

$U_{\mathrm{bn}}={\mathrm{Ri}}_b+L\frac{{\mathrm{di}}_b}{\mathrm{dt}}+e_b---\left(2\right)$

$U_{\mathrm{cn}}={\mathrm{Ri}}_c+L\frac{{\mathrm{di}}_c}{\mathrm{dt}}+e_c---\left(3\right)$

In formula, U _an, U _bn, U _cnrepresent the winding phase voltage of A, B, C three-phase respectively, e _a, e _b, e _cbe respectively the back-emf of ABC three-phase, i _a, i _b, i _cbe respectively the afterflow phase current of A, B, C three-phase.

Due to sustained diode 3 conducting, have again:

U _an＝U _bn(4)

Three characteristics of the middle term winding is Y-connection, therefore has:

i _a+i _b+i _c＝0 (5)

Inverter busbar voltage is U _dC, have:

U _an-U _cn＝U _DC(6)

Formula associating in (1)-(6) can be obtained the slope of afterflow phase:

$\frac{{\mathrm{di}}_b}{\mathrm{dt}}=\frac{U_{\mathrm{DC}}-{3\mathrm{Ri}}_b-(e_b-e_a)-(e_b-e_c)}{3L}---\left(7\right)$

Figure 4 shows that three opposite potential e of BLDC motor _a, e _b, e _cschematic diagram.Black surround part is the interval of A+B-commutation to A+C-.As seen from the figure, e _b-e _awith e _b-e _cbe monotonous descending function.By above-mentioned conclusion, ignore winding resistance pressure drop Ri _b, convolution (7) is known, and afterflow phase current slope is then monotonic increasing function, is beneficial to threshold values and compares.

Threshold values comparison algorithm as shown in Figure 5.Represent the enable logic of slope detection in figure in dotted line frame, its objective is that guaranteeing that slope threshold values detects only detects when freewheel current does not drop to zero, avoids pulse by mistake to export.This algorithm need meet two conditions simultaneously and just can compare by enable threshold values, and one is that the upper and lower bridge arm of tested phase turns off simultaneously, represents that this is afterflow phase mutually; Two are not equal to zero for the electric current of this phase, represent that afterflow not yet terminates, meet threshold values comparison condition.

Due to the current slope of afterflow phase on passing through when pipe afterflow and lower pipe afterflow symbol contrary.Namely, when freewheel current is greater than zero, current slope is less than zero; When freewheel current is less than zero, current slope is greater than zero.Conveniently threshold values compares, and the current slope of trying to achieve need be carried out signed magnitude arithmetic(al), then compares with pre-set threshold value and can obtain crossover point signal.

From Fig. 4 also can, at afterflow opposite potential e _b=0 place, has:

(e _b-e _a)+(e _b-e _c) _eb＝0＝0(8)

Formula (8) is brought into (7), can obtain:

${\frac{{\mathrm{di}}_b}{\mathrm{dt}}|}_{e_b=0}=\frac{U_{\mathrm{DC}}-3{\mathrm{Ri}}_b}{3L}\≈\frac{U_{\mathrm{DC}}}{3L}---\left(9\right)$

The schematic diagram that threshold values chooses can be obtained, as shown in Figure 6 according to above formula.As seen from the figure, this threshold values needs comparatively multi-parameter information, as busbar voltage U _dC, phase winding resistance R, equivalent d-axis inductance L etc.In actual application, winding resistance pressure drop can be ignored, or calculate threshold values to its injected pulse time static by motor.

The algorithm waveform schematic diagram that Fig. 7 (a) and Fig. 7 (b) are depicted as BLDC motor opposite potential when being difformity,

From top to bottom be respectively in figure: winding phase current, winding phase voltage compare pulse with back-emf, switching tube drive singal, current slope threshold values and current slope calculated value, threshold values.In Fig. 7 (a), counter potential waveform is close to trapezoidal wave, calculate through the enable logic shown in Fig. 5 and current slope, current slope during afterflow can be extracted, the reservation threshold calculated shown in itself and Fig. 6 is compared, the back-emf zero crossing of this phase can be obtained.

Due to design of electrical motor processing, the back-emf of most BLDC motor cannot present comparatively ideal trapezoidal wave, is often more partial to sinusoidal signal.When being ideal sine wave by the known winding back-emf of Fig. 7 (b), the current slope of afterflow phase is still monotonic function, and the estimate of situation of zero crossing is consistent with Fig. 7 (a).Describe the present invention and can be applicable to, on the nonideal BLDC motor of waveform back-emf, to there is stronger generality.

The algorithm scope of application of the present invention is the situation that under high rotating speed, heavy load, afterflow opposite potential zero crossing floods.When motor speed is lower, or during underloading, zero crossing no longer floods, and namely current slope does not also terminate, because the method is no longer applicable with the equal afterflow of setting threshold values.Meanwhile, traditional back-emf zero-crossing method is suitable for the occasion of not flooding with zero crossing by industrial quarters and experts and scholars' checking very much, and therefore the present invention effectively can supplement the scope of application of position-sensor-free algorithm on the basis of zero-crossing method.

The present invention coordinates to widen the flow chart of BLDC electric machine without position sensor algorithm as shown in Figure 8 with traditional zero-crossing method.After the commutation moment arrives, the electric current of Real-time Collection afterflow phase.When afterflow phase current does not drop to 0, solve the current slope of afterflow phase, and compare with the threshold values of setting, if current slope is equal with threshold values, the back-emf zero crossing representing afterflow phase is detected, and the position probing in this commutating period completes, and an exportable zero crossing pulse is to controller.As current slope afterflow phase current in the region being greater than threshold values drops to zero, illustrate that now zero crossing does not flood, systematic evaluation is to traditional zero-crossing method, and the pulse of same output zero crossing is to controller, and in this commutating period, position probing completes.The drive singal drive motors that crossover point signal can generate three phase inverter bridge through process in the controller runs.

In sum, under permanent-magnet brushless DC electric machine position-sensor-free algorithm of the present invention effectively can overcome motor high-speed overload situation, zero crossing floods the problem that cannot detect, and cooperatively interacts effectively can expand the working range of position-sensor-free algorithm with traditional zero-crossing method.Meanwhile, the method is without the need to changing electric machine structure, and lower to the opposite potential waveform requirements of motor.Therefore, the present invention has applied widely, has stronger using value.

Those skilled in the art of the present technique are understandable that, unless otherwise defined, all terms used herein (comprising technical term and scientific terminology) have the meaning identical with the general understanding of the those of ordinary skill in field belonging to the present invention.Should also be understood that those terms defined in such as general dictionary should be understood to have the meaning consistent with the meaning in the context of prior art, unless and define as here, can not explain by idealized or too formal implication.

Above-described embodiment; object of the present invention, technical scheme and beneficial effect are further described; be understood that; the foregoing is only the specific embodiment of the present invention; be not limited to the present invention; within the spirit and principles in the present invention all, any amendment made, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (2)

1. a driving method for permanent-magnet brushless DC electric machine position-sensor-free, is characterized in that comprising the following steps:

Step 1), when the commutation moment arrives, the electric current of Real-time Collection afterflow phase;

Step 2), the afterflow phase current according to collecting solves its current slope;

Step 3), calculate current slope threshold values corresponding to the afterflow phase current that collects according to the busbar voltage of three phase inverter bridge, the equivalent resistance of phase winding, the equivalent d-axis inductometer of phase winding;

Step 4), by step 2) in the current slope that calculates and step 3) in the current slope threshold values that calculates compare;

Step 4.1), when afterflow phase current does not drop to zero, current slope is equal with current slope threshold values, then export position detection signal during afterflow opposite potential zero crossing;

Step 4.2), if current slope is inequal with current slope threshold values yet when the electric current of afterflow phase drops to zero, adopt traditional zero-crossing method to detect, export position detection signal during back-emf zero crossing;

Step 5), position detection signal is carried out phase shift process, generates the drive singal of three phase inverter bridge;

Step 6), the drive singal drive motors according to three-phase inverter runs.

2. the driving method of permanent-magnet brushless DC electric machine position-sensor-free according to claim 1, is characterized in that, described step 3) in calculate the formula of current slope threshold values corresponding to the afterflow phase current that collects as follows:

$\frac{{\mathrm{di}}_k}{\mathrm{dt}}{|}_{e_k=0}=\frac{U_{\mathrm{DC}}-3{\mathrm{Ri}}_k}{3L}\≈\frac{U_{\mathrm{DC}}}{3L}$

In formula, k represents the afterflow phase in ABC three-phase, e _kfor the back-emf of afterflow phase, i _kfor afterflow phase current, U _dCfor the busbar voltage of inverter bridge, L is the equivalent d-axis inductance of brshless DC motor, and R is the phase resistance of brshless DC motor.