CN109546903B - Compensation method for voltage sampling offset of brushless direct current motor without position sensor - Google Patents

Abstract

The invention relates to a compensation method for voltage sampling offset of a position sensor-free brushless direct current motor, which is based on a back electromotive force method. Aiming at the problem, the invention analyzes the influence of voltage offset on zero-crossing point sampling according to the back electromotive force zero-crossing point information during the phase change period, and provides a compensation method for the voltage sampling offset of the brushless direct current motor without the position sensor. The compensation control system realized by the simulation means carries out corresponding compensation in the subsequent commutation period after the system calculates the error, and the result shows the feasibility and the effectiveness of the method.

Description

Compensation method for voltage sampling offset of brushless direct current motor without position sensor

Technical Field

The invention relates to a compensation method for voltage sampling offset of a brushless direct current motor without a position sensor, and belongs to the field of motor driving.

Background

Brushless dc motor is widely used in various fields such as household appliances, industrial equipment, unmanned aerial vehicles and electric vehicles because of having advantages such as high power density, high efficiency, low maintenance cost, simple structure and easy control. Brushless dc motors are driven by a three-phase inverter, typically using three hall sensors to provide six discrete rotor positions, control commutation control of the three-phase windings, and thus appropriate commutation. However, rotor position sensors increase cost and reduce reliability. Therefore, position sensor-less control methods have been developed over the last decade. The control method of the brushless dc motor without the position sensor mainly includes a back electromotive force method, a free wheel diode method, a flux linkage estimation method, and the like. Among them, the back electromotive force method brushless dc motor without position sensor is most widely used. The back electromotive force of the brushless direct current motor cannot be directly measured, and generally, a voltage sensor is used for sampling phase voltage or line voltage difference signals of the motor, then a filter is used for filtering out the line voltage difference or high-frequency interference in the phase voltage, and then the zero crossing point of the line voltage or the high-frequency interference is detected. However, due to the insufficient sensitivity of the voltage sensor and the zero drift of the operational amplifier in the filter circuit, the sampled line voltage difference or phase voltage signal often deviates to form an unbalanced zero crossing point, which affects the accurate phase commutation of the brushless dc motor, and the operating performance of the brushless dc motor is abnormal under severe conditions.

Disclosure of Invention

In view of the above prior art, the technical problem to be solved by the present invention is to provide a compensation method for voltage sampling offset of a brushless dc motor without a position sensor, which can solve unbalanced zero crossing points formed by voltage sampling offset.

In order to solve the technical problem, the invention provides a compensation method for voltage sampling offset of a brushless direct current motor without a position sensor, which comprises the following steps:

the method comprises the following steps: pre-positioning a rotor of the brushless direct current motor, applying phase change logic to the brushless direct current motor, and dragging the motor to a certain rotating speed;

step two: detecting a terminal voltage or line voltage difference signal of the brushless direct current motor, filtering the terminal voltage or line voltage difference signal, detecting a zero crossing point of the terminal voltage or line voltage difference signal, and forming three paths of virtual Hall signals T_a、T_b、T_c；

Step three: for three paths of virtual Hall signals T_a、T_b、T_cPerforming XOR operation to obtain T_posWherein T is_posThe rising edge and the falling edge of the counter electromotive force are the same as the zero point position of the counter electromotive force;

step four: calculating T_posIs high level for a time period t_θ1Calculating T_posIs of low level duration t_θ2；

Step five: using the current period t_θ1、t_θ2Calculating the rotating speed of the brushless direct current motor, wherein the rotating speed expression is as follows:

wherein p is the number of pole pairs of the motor;

step six: the counter electromotive force of the next period is zero-crossing point information T_a、T_b、T_cLag 0.5t_θ1-t_θfForm T_a'、T_b'、T_c'. Lag 0.5t_θ2-t_θfForm T_a”、T_b”、T_c", where t_θfLag time caused for filtering;

step seven: is carried out by_a＝T_a'∩T_a”、S_b＝T_b'∩T_b”、S_c＝T_c'∩T_c' operation, respectively obtaining commutation signals S_a、S_b、S_c；

Step eight: the phase-change signal generates the phase-change logic of the motor, and is input to the three-phase full-control inverter circuit to drive the motor to operate.

The invention has the beneficial effects that: compared with the prior art, the invention considers the influence of the voltage sensor and the operational amplifier circuit on the sampling of the position signal of the brushless direct current motor without the position sensor, can still accurately correct the unbalanced zero crossing point under the condition of insufficient sensitivity of the voltage sensor, and reduces the hardware cost.

Drawings

FIG. 1 is an equivalent circuit of a brushless DC motor;

FIG. 2(a) is a voltage sensor line voltage difference sampling waveform;

FIG. 2(b) is a voltage sensor line voltage difference sampling waveform;

FIG. 3 is a graph of the effect of voltage offset on zero crossing sampling;

FIG. 4 is a system diagram of a compensation algorithm;

FIG. 5 is a circuit diagram of a filter;

FIG. 6 shows a back EMF zero crossing signal and a commutation point signal;

fig. 7 is a waveform diagram of delay angle calculation.

Detailed Description

The invention is further described below with reference to the accompanying drawings:

based on a back electromotive force method, phase voltage or line voltage difference needs to be sampled in the process of acquiring position information by a brushless direct current motor without a position sensor, and the sampled line voltage difference or phase voltage signal is deviated due to insufficient sensitivity of a voltage sensor and zero drift of an operational amplifier in a filter circuit, so that unbalanced zero-crossing points are formed, the phase change of the motor is influenced, and the operation of the motor is seriously influenced. Aiming at the problem, the invention analyzes the influence of voltage offset on zero-crossing point sampling according to the back electromotive force zero-crossing point information during the phase change period, and provides a compensation method for the voltage sampling offset of the brushless direct current motor without the position sensor. The compensation control system realized by the simulation means carries out corresponding compensation in the subsequent commutation period after the system calculates the error, and the result shows the feasibility and the effectiveness of the method.

The invention relates to a compensation method for voltage sampling offset of a brushless direct current motor without a position sensor, which comprises the brushless direct current motor, a three-phase full-control inverter circuit, a position detection module, a controller, a voltage offset compensation module and a filtering compensation module, wherein the brushless direct current motor is connected with the three-phase full-control inverter circuit; the position detection module utilizes a voltage sensor to sample line voltage difference or phase voltage of the motor, filters high-frequency interference in the line voltage difference or the phase voltage through a filter, and generates phase change logic by detecting a zero crossing point. The filter compensation module compensates a lag angle caused by the filter, the controller includes a speed regulator and a current regulator, and the voltage offset compensation module compensates an unbalanced commutation signal caused by a voltage offset. The method comprises the following steps:

the method comprises the following steps: the brushless dc motor rotor is pre-positioned, and phase commutation logic is applied to the brushless dc motor to drive the motor to a certain rotational speed, typically about 300 rpm.

Step two: detecting the voltage difference of the terminal or the line of the brushless DC motor, filtering, detecting the zero crossing point of the voltage difference to form three paths of virtual Hall signals T_a、T_b、T_c。

Step three: for three paths of virtual Hall signals T_a、T_b、T_cPerforming XOR operation to obtain T_posWherein T is_posThe rising edge and the falling edge of (c) are the same as the back emf zero position.

Step four: when T is_posWhen 1, the high level duration t is calculated_θ1When T is_posWhen equal to 0, calculate the low level time t_θ2。

Step five: using the current period t_θ1、t_θ2Calculating the rotating speed of the brushless direct current motor, wherein the rotating speed expression is as follows:

where p is the number of pole pairs of the motor.

Step six: the counter electromotive force of the next period is zero-crossing point information T_a、T_b、T_cLag 0.5t_θ1-t_θfForm T_a'、T_b'、T_c'. Lag 0.5t_θ2-t_θfForm T_a”、T_b”、T_c". Wherein t is_θfThe lag time caused for filtering.

Step seven: is carried out by_a＝T_a'∩T_a”、S_b＝T_b'∩T_b”、S_c＝T_c'∩T_c' operation, respectively obtaining commutation signals S_a、S_b、S_c。

Step eight: the phase-change signal generates the phase-change logic of the motor, and is input to the three-phase full-control inverter circuit to drive the motor to operate.

The invention takes line voltage difference sampling as an example, as shown in fig. 1, when the brushless direct current motor is conducted two by two at 120 degrees, the line voltage difference equation of the motor is

In the figure, R and L represent the resistance and inductance of each phase winding (the inductance is the difference between the self inductance and the mutual inductance). u. of_a、u_b、u_cIs a phase voltage e_a、e_b、e_cIs a counter electromotive force, i_a，i_b，i_cIs the phase current.

Will u_bcAnd u_caAre subtracted to obtain

When the AC phase is conductive, the B phase is a non-conductive phase. I.e. have i_a+i_b+i_c＝0，e_a+e _c0. Is substituted into the formula (2) to obtain

The B phase is a non-conductive phase and the current is 0. I.e. 2e_b＝u_bc-u_ab. The back emf is related only to the line voltage difference. Therefore, the zero crossing point of the back electromotive force can be obtained by sampling the zero crossing point of the line voltage difference. Line voltage difference sampling at a certain speed in actual measurementAs shown in FIGS. 2(a) and 2(b), the peak value is 3.74V and the bottom value is-3.5V, so that there is a voltage shift of 0.12V.

The zero drift of the voltage sensor and the operational amplifier in the filter module produces unbalanced zero crossings. The traditional brushless DC motor without position sensor delays the phase commutation by 30 degrees after sampling the zero crossing point of the back electromotive force, but according to the method, the phase commutation point generated by the unbalanced zero crossing point is different in width. Fig. 3 shows a comparison of balanced zero-crossing detection and unbalanced zero-crossing detection. By referring to fig. 3, whether the zero-crossing points are balanced or not, the commutation point is at the middle position of two zero-crossing points, so the unbalanced zero-crossing point compensation method in the claims can be used to solve the problem of unbalanced zero-crossing point encountered in line voltage difference sampling, as shown in fig. 4, which is a system diagram of the method proposed by the claims.

Examples

In order to verify the effectiveness of the compensation method for the voltage sampling offset of the brushless direct current motor without the position sensor, the invention carries out simulation verification. The filtering used by the invention adopts second-order low-pass filtering, and the impedance parameters and the schematic diagram of the filtering circuit are shown in figure 5.

The method is characterized in that the traditional three-stage starting is adopted, a control program gives a period of time for electrifying any two-phase stator winding, the stator magnetic field drags the rotor to a specified position, the windings are sequentially electrified according to a switch table, and the brushless direct current motor is switched to operate under the control method without a position sensor after the rotating speed of the brushless direct current motor is increased to a certain value. The current rotation speed is calculated by the rotation speed calculation method in the claims. And calculating a lag angle caused by filtering according to the filter parameters of the circuit, wherein alpha is a system damping coefficient, and omega₀Is the system natural frequency, omega is the angular velocity, theta_fThe (omega) is the phase delay angle, and the specific calculation formula is as follows

Three-path zero-crossing point signal T generated by zero crossing after line voltage difference filtering_a、T_b、T_cAs shown in fig. 6, the signal processing is performed according to the method of the claims, and the commutation delay angle calculation is as shown in fig. 7. Comparing commutation signals S generated by a position-sensorless in a simulation_aWith commutation signal H generated by position sensor_a，S_aAnd H_aThe corrected commutation signal of the brushless DC motor without the position sensor can replace commutation information provided by the position sensor and accurately commutate, so that the compensation method of the voltage sampling offset of the brushless DC motor without the position sensor can solve the zero-crossing point imbalance phenomenon caused by the voltage offset generated by sampling and filtering.

Claims (1)

1. A compensation method for voltage sampling offset of a brushless direct current motor without a position sensor is characterized by comprising the following steps:

the method comprises the following steps: pre-positioning a rotor of the brushless direct current motor, applying phase change logic to the brushless direct current motor, and dragging the motor to a certain rotating speed;

step two: detecting a terminal voltage or line voltage difference signal of the brushless direct current motor, filtering the terminal voltage or line voltage difference signal, detecting a zero crossing point of the terminal voltage or line voltage difference signal, and forming three paths of virtual Hall signals T_a、T_b、T_c；

Step three: for three paths of virtual Hall signals T_a、T_b、T_cPerforming XOR operation to obtain T_posWherein T is_posIs rising ofThe edge and the falling edge are the same as the zero position of the back electromotive force;

step four: calculating T_posHigh level duration t_θ1Calculating T_posLow level duration t_θ2；

Step five: using the current period t_θ1、t_θ2Calculating the rotating speed of the brushless direct current motor, wherein the rotating speed expression is as follows:

wherein p is the number of pole pairs of the motor;

step six: the next period of the three paths of virtual Hall signals T_a、T_b、T_cLag 0.5t_θ1-t_θfForm T_a'、T_b'、T_c', will T_a、T_b、T_cLag 0.5t_θ2-t_θfForm T_a”、T_b”、T_c", where t_θfLag time caused for filtering;

step seven: is carried out by_a＝T_a'∩T_a”、S_b＝T_b'∩T_b”、S_c＝T_c'∩T_c' operation, respectively obtaining commutation signals S_a、S_b、S_c；

Step eight: the phase-change signal generates the phase-change logic of the motor, and is input to the three-phase full-control inverter circuit to drive the motor to operate.

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