阅读说明：本技术 一种高动态性的无刷直流电机内功角控制方法 (High-dynamic internal power angle control method for brushless direct current motor ) 是由 谭博 郭兴媛 刘卫国 陈哲 王西坡 于 2019-09-17 设计创作，主要内容包括：本发明涉及一种高动态性的无刷直流电机内功角控制方法,在相端电压与1/2母线电压的理想反电势过零点,判断提取有效过零点。由于反电势过零点前后,端电压和1/2母线电压的积分差可以检测内功角大小,故计算并锁存积分值,通过PI调节,到实时超前角,对前后积分差进行控制,达到减小内功角目的。本发明考虑到换相过程二极管续流对端电压波形产生的干扰,得到准确换向点。然后确定补偿角,在理想换向点的基础上超前换相,从而减小了内功角,提高了电机功率密度和效率,根据端电压的变化实时补偿内功角,具有很高的动态性。实验表明,与传统方法相比,该方法下内功角得以减小,功率密度提高,电流减小,最大电流可以减小4.9％,铜损降低10％。(The invention relates to a high-dynamic brushless direct current motor internal power angle control method, which judges and extracts an effective zero crossing point at an ideal back electromotive force zero crossing point of phase end voltage and 1/2 bus voltage. The integral difference between the terminal voltage and 1/2 bus voltage before and after the back emf zero crossing point can detect the internal power angle, so the integral value is calculated and latched, and the integral difference before and after real-time advance angle is controlled through PI adjustment, thereby achieving the purpose of reducing the internal power angle. The invention considers the interference of diode freewheeling on the voltage waveform of the terminal end in the phase change process to obtain an accurate commutation point. And then determining a compensation angle, and carrying out advanced phase commutation on the basis of an ideal commutation point, thereby reducing the internal power angle, improving the power density and efficiency of the motor, compensating the internal power angle in real time according to the change of the terminal voltage, and having high dynamic property. Experiments show that compared with the traditional method, the method has the advantages that the internal power angle is reduced, the power density is improved, the current is reduced, the maximum current can be reduced by 4.9%, and the copper loss is reduced by 10%.)

1. A high dynamic brushless DC motor internal power angle control method is characterized by comprising the following steps:

step 1: under the working condition of a non-commutation stage, the zero crossing point of the ideal back electromotive force is the intersection point of the voltage of the phase end and the voltage of the 1/2 bus;

step 2: screening effective zero-crossing points from the zero-crossing points detected by the method in the step 1, and eliminating invalid zero-crossing points caused by interference voltage;

three opposite potentials are in six interval states.

1: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is greater than 0;

2: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is greater than 0;

3: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is less than 0;

4: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is less than 0;

5: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is less than 0;

6: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is greater than 0;

because the diode freewheeling causes the terminal voltage to generate interference pulses, if the method of the step one is adopted, three zero-crossing points can be detected, and the first two zero-crossing points caused by the interference voltage are invalid; the third time is the effective zero crossing point; detecting 6 effective zero-crossing points in six interval states;

and step 3: calculating the area of a triangle before and after each effective zero crossing point in the phase commutation process:

one triangle is formed by enclosing the terminal voltage and half of the bus voltage in the period from the beginning of phase change to the zero crossing point of counter potential and is marked as S_2yY is 1-6; the other triangle is formed by enclosing the terminal voltage and half of the bus voltage in the time from the counter potential zero crossing point to the commutation ending point and is marked as S_2y-1，y＝1～6；

In the three-phase counter electromotive force, each counter electromotive force zero-crossing point corresponds to two triangles and one area difference, so that in a complete interval mentioned in the step 1, six counter electromotive force zero-crossing points are provided, corresponding to 12 triangle areas, and 6 area differences delta S_y，y＝1～6；

State 1: delta S₁＝S₂-S₁

State 2: delta S₂＝S₄-S₃

State 3: delta S₃＝S₆-S₅

And 4: delta S₄＝S₈-S₇

And state 5: delta S₅＝S₁₀-S₉

And 6: delta S₆＝S₁₂-S₁₁

Wherein the content of the first and second substances,

in the formula: s_2y-1Representing the graph area enclosed by the terminal voltage and the half bus voltage before the back emf zero crossing point of the phase change stage; s_2yRepresenting the graph area enclosed by the terminal voltage and the half bus voltage after the counter potential zero crossing point of the phase change stage; u. of_cMRepresents the voltage of the C phase terminal; u represents the bus voltage; Δ t_2y-1The time difference between the phase change start and the back emf zero crossing point; Δ t_2yThe phase difference from the back emf zero crossing point to the end of the commutation; a. the₁Is the fundamental wave amplitude after three-phase back-emf Fourier decomposition, A_2n+1The harmonic component amplitude of the odd term after the three-phase back electromotive force Fourier decomposition is obtained; θ is the electrical angle of the motor rotor; omega is the angular speed of the rotor;

and 4, step 4: by Delta S_yThe phase change lead angle is updated, and is reduced to be near 0 through PI control, so that the internal power angle is reduced;

by Delta S_yAs the input of the PI controller, 0 is given by the PI controller, the output of the PI controller is used as the phase change advance angle of the motor, so that the motor is advanced for phase change, and therefore, in the next period, the area difference delta S formed by the enclosed end voltage and counter potential before and after the counter potential zero crossing point in the phase change process_yThe phase difference between the back electromotive force and the phase current of the motor is reduced to be 0, and the effect of reducing the internal power angle is achieved.

Technical Field

The invention belongs to a power angle control method in a brushless direct current motor, and relates to a high-dynamic power angle control method in the brushless direct current motor, which comprises a back electromotive force detection method without filter delay and a high-dynamic lead angle control method independent of motor parameters, and finally achieves the purpose of reducing an internal power angle.

Background

The brushless direct current motor has the advantages of high efficiency and high power density, and is particularly suitable for occasions with strict limits on weight and volume. In order to further improve the power density of the motor and reduce the weight and the volume of the motor, the brushless direct current motor is developed towards a high speed direction, and because the rotating speed of the motor is high, and the rotating speed of the motor is considered by the operation speed and the cost of a processor, the high speed brushless direct current motor generally adopts a driving method based on the voltage regulation of a front-stage Buck circuit and the phase conversion of a rear-stage three-phase six-state. Meanwhile, for safety reasons, the high-speed brushless dc motor generally employs a position-free control method based on back emf zero-crossing detection.

However, the detection error and filtering delay of the counter potential zero crossing point, the driving method of the three-phase six-state, and the first-order lag link formed by the motor resistance and the inductance, which exist in the conventional no-position method for counter potential zero crossing detection, all cause the increase of the internal power angle of the motor. When the load torque is constant, the increased internal power angle causes an increase in motor phase current and torque ripple. And, the internal power angle increases with increasing motor load, resulting in a reduction in the motor speed regulation range and power density.

The current methods for reducing the position error of the rotor mainly include the following steps: firstly, observing the position of a rotor by adopting a characteristic rule of ideal terminal voltage in a phase change process, for example, obtaining the position of the rotor by utilizing the symmetrical terminal voltage of a non-electrified phase generated at the beginning and the end of the commutation or detecting the terminal voltage difference between the beginning and the end of a commutation period, but neglecting the influence of a diode follow current process on the terminal voltage amplitude of the phase after the phase change is finished, thereby causing the essential difference of the terminal voltage or the line voltage before and after the phase change; secondly, considering the terminal voltage interference caused by phase change, a low-pass filter is adopted to filter the terminal voltage, but the terminal voltage is delayed by the zero crossing point of counter potential, so that the phase change is delayed. In this case, it is necessary to additionally compensate for the filter delay, for example, to compensate for a lag angle caused by the low pass filter based on a linear relationship between a parameter of the detection circuit and the frequency of the back electromotive force, or to calculate a phase delay caused by the low pass filter based on a filter parameter and the rotational speed of the motor, which are sensitive to a circuit parameter and have poor dynamics.

At present, there are several methods for reducing the internal power angle as follows: the first method is to observe the internal power factor angle error through a phase-locked loop and adjust the error to be zero through a PI regulator, but the method needs software phase discrimination and is complex in algorithm realization, and the second method is to calculate the real-time advance angle according to the phase current, the inductance and the flux linkage established by a motor magnet, but is sensitive to motor parameters, complex in calculation and poor in dynamic property.

Disclosure of Invention

Technical problem to be solved

In order to avoid the defects of the prior art, the invention provides a high-dynamic internal power angle control method of a brushless direct current motor, which is a high-dynamic internal power angle control method independent of motor parameters and high dynamics, and comprises a detection method for accurately determining a phase change point and an advance angle compensation method.

Technical scheme

A high dynamic brushless DC motor internal power angle control method is characterized by comprising the following steps:

step 1: under the working condition of a non-commutation stage, the zero crossing point of the ideal back electromotive force is the intersection point of the voltage of the phase end and the voltage of the 1/2 bus;

step 2: screening effective zero-crossing points from the zero-crossing points detected by the method in the step 1, and eliminating invalid zero-crossing points caused by interference voltage;

three opposite potentials are in six interval states.

1: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is greater than 0;

2: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is greater than 0;

3: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is less than 0;

4: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is less than 0;

5: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is less than 0;

6: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is greater than 0;

because the diode freewheeling causes the terminal voltage to generate interference pulses, if the method of the step one is adopted, three zero-crossing points can be detected, and the first two zero-crossing points caused by the interference voltage are invalid; the third time is the effective zero crossing point; detecting 6 effective zero-crossing points in six interval states;

and step 3: calculating the area of a triangle before and after each effective zero crossing point in the phase commutation process:

one triangle is formed by enclosing terminal voltage and half bus voltage in the period from the beginning of phase change to the zero crossing point of counter potential and is marked as S_2yY is 1-6; the other triangle is formed by the enclosure of the end voltage and half of the bus voltage in the time from the counter potential zero crossing point to the phase change ending point and is marked as S_2y-1，y＝1～6；

In the three-phase counter electromotive force, each counter electromotive force zero-crossing point corresponds to two triangles and one area difference, so that in a complete interval mentioned in the step 1, six counter electromotive force zero-crossing points are provided, corresponding to 12 triangle areas, and 6 area differences delta S_y，y＝1～6；

State 1: delta S₁＝S₂-S₁

State 2: delta S₂＝S₄-S₃

State 3: delta S₃＝S₆-S₅

And 4: delta S₄＝S₈-S₇

And state 5: delta S₅＝S₁₀-S₉

And 6: delta S₆＝S₁₂-S₁₁

Wherein the content of the first and second substances,

in the formula: s_2y-1Representing the graph area enclosed by the terminal voltage and the half bus voltage before the back emf zero crossing point of the phase change stage; s_2yRepresenting a graphical area enclosed by the terminal voltage and the half bus voltage after the counter potential zero crossing point of the phase change stage; u. of_cMRepresents the voltage of the C phase terminal; u represents the bus voltage; Δ t_2y-1The time difference between the phase change start and the back emf zero crossing point; Δ t_2yThe phase difference from the back emf zero crossing point to the end of the commutation; a. the₁Is the fundamental wave amplitude after three-phase back-emf Fourier decomposition, A_2n+1The harmonic component amplitude of the odd term after the three-phase back electromotive force Fourier decomposition is obtained; θ is the electrical angle of the motor rotor; omega is the angular speed of the rotor;

and 4, step 4: by Delta S_yThe phase change lead angle is updated, and is reduced to be near 0 through PI control, so that the internal power angle is reduced;

by Delta S_yAs the input of the PI controller, 0 is given by the PI controller, the output of the PI controller is used as the phase change advance angle of the motor, so that the motor is advanced for phase change, and therefore, in the next period, the area difference delta S formed by the enclosed end voltage and counter potential before and after the counter potential zero crossing point in the phase change process_yThe phase difference between the back electromotive force and the phase current of the motor is reduced to be 0, and the effect of reducing the internal power angle is achieved.

Advantageous effects

The high-dynamic internal power angle control method of the brushless direct current motor reduces the internal power angle between the phase current and the counter potential as much as possible and improves the power density. The invention provides a method for setting a lead angle before an ideal phase change point to lead a motor to change the phase in advance. The method comprises the steps of firstly, obtaining an ideal back electromotive force zero crossing point through a terminal voltage zero crossing rule, and thus obtaining an ideal reversing point; and then PI adjustment is carried out on the difference value of the two integrals according to the relation between the integral difference of the terminal voltage and 1/2 bus voltage and the internal power angle before and after the counter potential zero crossing point, so that the integral difference is reduced, and the internal power angle is reduced. Therefore, to achieve the purpose of reducing the internal power angle, two parts are needed: the first part is to obtain accurate and delay-free commutation point, and the second part is to control the lead angle to compensate the lead angle.

The technical scheme for solving the technical problems of the invention is as follows: first an ideal back-emf zero-crossing needs to be found. And the theoretical back-emf zero-crossing point is obtained by deducing voltage equations of the front end and the back end of the phase change, namely the intersection point of the voltage of the phase end and the voltage of the 1/2 bus. Due to the influence of diode freewheeling, invalid zero-crossing points can be generated in the detected back emf zero-crossing points, but the detected zero-crossing points are distributed according to a rule of an effective zero-crossing point and two invalid zero-crossing points, so that the effective zero-crossing points can be extracted through software logic judgment by utilizing the rule. The back emf zero crossing point leads by 30 degrees, thus obtaining the accurate phase-changing point. By adopting a high-dynamic lead angle compensation method, the integral difference between the end voltage and the 1/2 bus voltage before and after the back-emf zero-crossing point can detect the internal power angle, so that the integral value is calculated and latched, and the integral difference before and after the real-time lead angle is controlled through PI adjustment, so that the system is controlled in real time, and the aim of reducing the internal power angle is fulfilled.

The invention has the beneficial effects that: the internal power angle control method provided by the invention firstly ensures the accuracy of the counter potential zero crossing point, namely the accuracy of an ideal commutation point, and the method fully considers the interference generated by the voltage waveform of the diode freewheeling terminal end in the phase commutation process by utilizing the actual counter potential characteristic in the acquisition process, and does not depend on motor parameters to obtain the accurate commutation point. Then the characteristics of the end voltage before and after the back electromotive force zero crossing point are analyzed, the compensation angle is determined, and the phase commutation is advanced on the basis of the ideal commutation point, so that the internal power angle is reduced, the power density and the efficiency of the motor are improved, the internal power angle is compensated in real time according to the change of the end voltage, and the dynamic performance is high. Experiments show that compared with the traditional method, the method has the advantages that the internal work angle is reduced, the power density is improved, the current is reduced, the maximum current can be reduced by 4.9%, and the copper loss is reduced by 10%.

Drawings

FIG. 1: power supply topology structure of high-speed BLDCM

FIG. 2: is a schematic diagram between ideal three-phase terminal voltage and zero-crossing point voltage; wherein u is_xMIs the voltage at the x-phase terminal; u. of_xZPFor the zero crossing waveform of the voltage at the x-phase end, U/2 is 1/2 bus voltage, and x is a, b and c

FIG. 3: the relation between the three-phase terminal voltage and the back emf zero crossing point; wherein u is_xMIs the voltage at the x-phase terminal; u. of_xZPFor the zero crossing waveform of the voltage at the x-phase end, U/2 is 1/2 bus voltage, and x is a, b, c and S_1-12Is marked with the area of a triangle, Delta theta₁For the phase difference between the start of commutation and the zero-crossing of the back-emf, Δ θ₂For phase difference between zero-crossing of counter potential and end of commutation

FIG. 4: 0.08Nm,12000r/min-24000 r/min; wherein u is_cMIs the voltage of the phase C terminal; i.e. i_cIs C phase current; u. of_cZPZero crossing voltage for the opposite potential of C;is an internal power angle

FIG. 5: 0.08Nm,12000r/min-24000 r/min; wherein u is_cMIs the voltage of the phase C terminal; i.e. i_cIs C phase current; u. of_cZPZero crossing voltage for the opposite potential of C;is an internal power angle

Detailed Description

The invention will now be further described with reference to the following examples and drawings:

the basic idea of the invention is to set a lead angle before the ideal phase-changing point of the high-speed brushless DC motor to make the motor change the phase in advance, thereby reducing the internal power angle and improving the power density and the operation efficiency.

The invention relates to a high-dynamic brushless direct current motor internal power angle control method independent of motor parameters, which mainly comprises two parts, wherein one part is a back electromotive force zero crossing point detection method without filter delay, and the other part is compensation of a lead angle, so that an internal power angle is reduced. The method is implemented according to the following steps:

step 1: and finding a theoretical back-emf zero-crossing point, namely the intersection point of the phase end voltage and 1/2 bus voltage, according to the working condition of the non-commutation stage.

The power topology of the high speed BLDCM is shown in fig. 1.

In the non-commutation phase, for example, when the A phase upper tube and the B phase lower tube are turned on and the C phase is turned off, the three-phase voltage equation can be expressed as

i_x(x ═ a, b, c) for phase currents, u_xMIs the voltage of the x-phase terminal, R is the motor winding, L is the motor inductance, e_xIs the x phase counter potential. u. of_NMIs the neutral point voltage. (x ═ a, b, c)

The power device is in a saturated conducting state, the tube voltage drop of the power device can be ignored and obtained,

u is the bus voltage, e_a、e_bA, B opposite potential.

Then

e_x(x ═ a, B, C) denotes a, B, C three-phase back-emf, u_NMIs the neutral point voltage.

When three-phase windings of the brushless direct current motor are symmetrical, the three-phase counter electromotive force of the motor is trapezoidal wave, and Fourier expansion is carried out on the trapezoidal wave

A₁Is the amplitude of the fundamental voltage after back-emf Fourier decomposition, A_2n+1The amplitude of the 2n +1 th voltage after Fourier decomposition is shown, and theta is the electrical angle of the motor rotor.

λ_pω_mIs trapezoidal wave peak value of brushless DC motor, wherein_mFor mechanical angular velocity, λ, of the motor_pIs a coefficient, λ_pN is the number of series conductors per phase, B is the magnetic flux density in the field region in which the conductors are located, r is the rotor outer diameter, and N is the harmonic order.

When theta is 2 pi/3 or-pi/3, the voltage of the C-phase terminal obtained by substituting (4) into (3) is as follows:

u_cMrepresents the C-phase terminal voltage and U represents the bus voltage.

Therefore, the intersection point of the voltage at the C phase end and the voltage of the half bus is the zero crossing point of the opposite potential of C. Because three phases are symmetrical, the intersection point of the voltage zero-crossing point of the phase A and the phase B and the voltage of one half of the bus is the phase A and the phase B opposite potential zero-crossing point

Therefore, the counter potential acquisition method is provided as follows: firstly, three-phase terminal voltage and U/2(U is bus voltage) pass through a comparator, when the terminal voltage is higher than the U/2, the output is 1, and when the terminal voltage is lower than the U/2, the output is 0, so that high and low levels capable of reflecting a reverse potential zero-crossing state can be obtained; and then detecting the rising edge and the falling edge of the counter potential zero-crossing state to obtain the edge triggering time, wherein the triggering time is the zero-crossing point of the three-phase counter potential. The three-phase back emf zero-crossings are shown as black circles in fig. 2.

Step 2: and (4) screening effective zero-crossing points from the zero-crossing points detected by the method in the step one, and eliminating invalid zero-crossing points caused by interference voltage.

In the phase change stage, assuming that the C-phase lower tube is turned off and the upper tube diode freewheels, which may cause interference pulses to appear in the terminal voltage, if the method proposed in step one is still followed, i.e., the intersection point of the terminal voltage and the 1/2 bus voltage is taken as a counter potential zero crossing point, invalid zero crossing points caused by some interference voltages may be detected.

The relationship between the actual three-phase terminal voltage and the zero-crossing point voltage is shown in fig. 3. As can be seen from fig. 2, in one on period, there are 6 effective zero-crossing points, so corresponding to fig. 3, the effective zero-crossing points are six black dots, and the ineffective zero-crossing points are 12 black square dots in fig. 3.

Recording the actual counter potential of the A phase as E_AThe actual counter potential of the phase B is E_BThe actual counter potential of phase C is E_C。

Recording the reverse potential A acquired in the step one as E_A', opposite potential E of B taken_B', counter potential E of collected C_C'。

The actual counter electromotive force phases of the three phases are 120 degrees different from each other, and the counter electromotive force zero-crossing state of the three phases has six state intervals in a complete cycle, as shown in fig. 2.

State interval 1: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is greater than 0, (namely E)_A＜0,E_B＜0,E_C＞0)。

State section 2: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is greater than 0, (namely E)_A＞0,E_B＜0,E_C＞0)。

State section 3: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is less than 0, and the actual counter potential of the phase C is less than 0, (namely E)_A＞0,E_B＜0,E_C＜0)。

State section 4: the actual counter potential of the phase A is greater than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is less than 0, (namely E)_A＞0,E_B＞0,E_C＜0)。

State interval 5: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is less than 0, (namely E)_A＜0,E_B＞0,E_C＜0)。

State section 6: the actual counter potential of the phase A is less than 0, the actual counter potential of the phase B is greater than 0, and the actual counter potential of the phase C is greater than 0, (namely E)_A＜0,E_B＞0,E_C＞0)。

Under the six combinations, the terminal voltage interference voltage caused by diode freewheeling is respectively collected to obtain the jump edges of the three-phase back emf zero-crossing state, and the comparison of the actual back emf state and the collected back emf state in the state combinations can be known, the zero-crossing point detected in an actual back emf state interval is caused by the interference pulse, the obtained zero-crossing point is invalid, and the zero-crossing point detected in the third time interval is valid.

In the six counter-potential combination states, this rule is all true. Therefore, according to the rule, effective zero crossing points can be extracted by numbering the detected zero crossing points and then screening through software logic.

And step 3: and calculating two triangular areas enclosed by the front and rear end voltages of the effective back electromotive force zero crossing point and one half of the bus voltage in each phase commutation process.

When the internal work angle isCounter potential phase theta_eEqual to current phase theta_iThat is, the zero-crossing of the back emf coincides with the zero-crossing of the phase current. Due to the three-phase six-state working mode of the brushless direct current motor, the phase current is similar to a square wave. In each conducting period, two turn-off regions, namely two zero-potential platforms, exist in the phase-change stage, and no definite zero-crossing point exists, and the zero-crossing point of the phase current can be described as the midpoint of the turn-off region of the phase current. It is thus obtained that the zero crossing of the counter potential coincides with the midpoint of the phase current off region when the internal power angle is zero.

The time difference between the start of the commutation (i.e. the start of the phase current off-state region) and the zero-crossing of the back-emf is thus recorded as Δ t_2y-1The time difference between the zero-crossing point of the back emf and the end of the commutation (i.e., the end of the phase current off region) is Δ t_2y. From the above analysis, Δ t when the internal power angle is equal to zero_2y-1＝Δt_2y(ii) a When the internal power angle is greater than zero (i.e., back-emf leads phase current), the back-emf zero-crossing point is before the midpoint of the phase current off region, at_2y-1＜Δt_2y(ii) a When the internal power angle is less than zero (i.e. the back-emf lags the phase current), the back emf zero-crossing point is in the phase current off regionAfter the middle of the domain, Δ t_2y-1＞Δt_2y。

It can be seen that to achieve the effect of the internal power angle of 0 proposed herein, Δ t is required_2y-1＝Δt_2y. However, when the speed changes suddenly, the terminal voltage amplitude and the commutation time are affected, and as can be seen from formula 6, the area integration can make the change of the voltage amplitude offset the change of the commutation time, so the change of all variables is taken into account through the area integration, and the change is recorded as S_2y-1The area of a triangle formed by the voltage of the front end of the back emf zero crossing point and the voltage of the 1/2 bus; s_2yThe area of a triangle formed by the end voltage after the counter potential zero crossing point and the 1/2 bus voltage is shown.

The area difference can be calculated as:

wherein S is_2y-1Representing the graph area enclosed by the terminal voltage and the half bus voltage before the back emf zero crossing point of the phase change stage; s_2yRepresenting a graphical area enclosed by the terminal voltage and the half bus voltage after the counter potential zero crossing point of the phase change stage; u. of_cMRepresents the voltage of the C phase terminal; u represents the bus voltage; Δ t_2y-1The time difference between the phase change start and the back emf zero crossing point; Δ t_2yThe phase difference from the back emf zero crossing point to the end of the commutation; a. the₁Is the fundamental wave amplitude after three-phase back-emf Fourier decomposition, A_2n+1The harmonic component amplitude of the odd term after the three-phase back electromotive force Fourier decomposition is obtained; θ is the electrical angle of the motor rotor; ω is the rotor angular velocity.

Wherein λ is_pω_mThe trapezoidal wave peak value of the brushless direct current motor is obtained. Wherein ω is_mThe mechanical angular speed of the motor; lambda [ alpha ]_pIs a coefficient, λ_pNBlr. N is the number of the series conductors of each phase; b is the magnetic flux density in the field region where the conductor is located; r is the rotor outer diameter; n is a harmonic orderAnd (4) counting.

As can be seen from equation (6), if the rotation speed is constant, Δ t_2y＝Δt_2y-1When Δ S is 0; if the rotation speed changes, the commutation time is inversely proportional to the rotation speed, Δ t_2y≠Δt_2y-1However, the terminal voltage is in direct proportion to the rotating speed and can change in opposite direction to the commutation time, and finally the value of delta S is not influenced. Therefore, to achieve the effect of the internal power angle of 0 proposed herein, it is sufficient to ensure that Δ S is 0.

Therefore, the difference of two triangular areas formed by the end voltage and the half bus voltage before and after the effective back electromotive force zero crossing point in the three-phase commutation process can be calculated, and the lead angle is updated according to the area difference. After the phase change of each phase is completed, the integration module calculates the area difference according to a formula (6), and data latch is carried out on the area difference and transmitted to the PI module, and the PI module generates a corresponding lead angle.

The relationship between the three-phase terminal voltage and the zero-crossing point of the counter potential is shown in FIG. 4.

The complete commutation process of the three-phase terminal voltage is divided into A-R18 areas. As shown in fig. 4, a region is divided when the state of the zero-crossing point waveform of any phase end changes once;

the region A + B is from the beginning of phase inversion in phase A to the end of phase inversion in phase A. At the moment, integral calculation is carried out in the area A + B by using a formula (6) to obtain a triangular area difference delta S formed by the surrounding of the terminal voltage and one half of the bus voltage before and after the back electromotive force zero crossing point in the phase-changing process of the phase A₁。

The region C is the C-phase diode freewheeling stage before the phase conversion of A is finished and the phase conversion of C is started, and the stage calculates Delta S₁＝S₂-S₁。

The region D + E is from the beginning of the C-phase commutation to the end of the C-phase commutation. At the moment, in the region D + E, the triangular area difference Delta S enclosed by the terminal voltage and the half bus voltage before and after the back emf zero crossing point is obtained by calculation according to the formula (6)₂。

The region F is the B-phase diode freewheeling stage before the C-phase commutation is finished and the B-phase commutation is started, and the stage finishes calculating data deltaS₂Latching and clearing.

The region G + H is from the beginning of the B-phase commutation to the end of the B-phase commutation. At the moment, in the region G + H, calculation is carried out by using a formula (6) to obtain a triangular area difference delta S formed by the surrounding of the terminal voltage and one half of the bus voltage before and after the back electromotive force zero crossing point in the phase-change process of the B phase₃。

The region I is the A-phase diode freewheeling stage before the phase change of B phase is finished and the phase change of A phase is started, and the stage finishes calculating data Delta S₃Latching and clearing.

The region J + K is from the beginning of phase inversion to the end of phase inversion. At the moment, in the area J + K, the formula (6) is used for calculating to obtain a triangular area difference delta S formed by the surrounding of the terminal voltage and one half of the bus voltage before and after the back electromotive force zero crossing point in the phase-A commutation process₄。

The region L is a C-phase diode freewheeling stage before the phase change of A is finished and the phase change of C is started, and the stage finishes calculating data Delta S₄Latching and clearing.

The region M + N is from the C-phase commutation to the C-phase commutation. At the moment, in the region M + N, the formula (6) is used for calculation to obtain a triangular area difference delta S formed by the end voltage and one-half bus voltage before and after the back emf zero crossing point in the C-phase commutation process₅。

The region O is a B-phase diode freewheeling stage before the C-phase commutation is finished and the B-phase commutation is started, and the stage finishes calculating data Delta S₅Latching and clearing.

The region P + Q is from the phase change of B to the phase change of B. At the moment, in the region P + Q, the formula (6) is used for calculation to obtain a triangular area difference delta S formed by the end voltage and one-half bus voltage before and after the back electromotive force zero crossing point in the phase-changing process of the B phase₆。

The region R is the A-phase diode freewheeling stage before the phase change of B is finished and the phase change of A is started, and the stage finishes calculating data Delta S₆Latching and clearing.

And 4, step 4: Δ S calculated by step three_yThe phase change lead angle is updated and reduced to 0 by PI control, thereby reducing the internal power angle.

From step three, the basic purpose of the controller is to adjust Δ S_y0. Therefore, it is expressed by Δ S_yAs the input of the PI controller, 0 is given by the PI controller, the output of the PI controller can be used as a phase change advance angle of the motor to advance the phase change of the motor, so that the area difference delta S formed by the surrounding of the terminal voltage and the counter potential before and after the counter potential zero crossing point in the phase change process is used as the area difference delta S of the counter potential in the next period_yThe phase difference between the back electromotive force and the phase current of the motor is reduced to be 0, and the effect of reducing the internal power angle is achieved.

After the internal power angle control is carried out by the method, the average value of the internal power angle is 0 in one conducting period. And the average value of the power angle in a 60-degree conduction period is kept to be zero in the process of changing the working state of the motor.

The simulation results are shown in fig. 4 and 5. When the motor load is kept to be 0.08Nm and the rotating speed is changed from 12000r/min to 24000r/min, the waveform diagram and the internal power angle waveform of the traditional method are shown in FIG. 4; the waveform under the proposed method is shown in fig. 5.

Simulation proves that the internal power angle of the traditional method is smaller than zero, and the internal power angle cannot be dynamically adjusted when the rotating speed changes; the method can effectively adjust the internal power angle in real time, can quickly adjust when the rotating speed changes, and ensures that the average internal power angle is 0.