A brushless motor current sampling method and brushless motor control mechanism

Abstract

The present invention discloses a brushless motor current sampling method and a brushless motor control mechanism. The control mechanism includes an inverter circuit and a control circuit. The inverter circuit includes at least two bridge arms, the bridge arms are a first bridge arm and a second bridge arm. The control circuit controls the upper and lower switch tubes of the first bridge arm and the second bridge arm to be turned on in at least one state, and adopts different bus current values, and determines the initial position of the rotor according to the current value. After the upper switch tube of the first bridge arm and the lower switch tube of the second bridge arm are controlled to be turned on at the same time for a first predetermined time, the first current value can be collected, and the upper switch tube of the first bridge arm is turned off, while the lower switch tube of the second bridge arm continues to be turned on, and the lower switch tube of the second bridge arm is turned off after the second predetermined time is turned on, so as to reduce the peak voltage. The patent of the present invention realizes current sampling and motor positioning in a simple form, reduces the peak voltage, and thus reduces the voltage applied to both ends of the switch tube, which can reduce the requirements of the switch tube and reduce the cost.

Description

[Technical field]

[0001] The present invention relates to the technical field of brushless motor control, and in particular to a brushless motor current sampling method and a brushless motor control mechanism. [Background Technology]

[0002] In order to start the brushless motor, it is necessary to determine the initial position of the rotor. The permanent magnet motor detects the position of the rotor through the Hall sensor, but the position sensor is expensive, so the brushless sensorless motor is widely used. The position sensorless control method does not use the position sensor. It can detect the bus current and switch the switch tube of the inverter circuit in different combinations. The positive and negative voltages are passed through any two-phase windings, and the bus current is taken respectively. According to the relationship between the currents, the initial position of the rotor is determined. When the switch tube is disconnected for switching, the current cannot change suddenly because the motor winding is inductive, and there will be a continuous current process, such as Figure 6 As shown in the schematic diagram of the known freewheeling current flow direction, if the UV phase is turned on first (Q1Q5 is turned on), when the UV phase is turned off for switching, since the motor is an inductive load, the current flowing through the UV phase winding cannot change suddenly, and the current flows through the diode D4, the U phase winding, the V phase winding, and the diode D2 for freewheeling. At this time, the voltage of the V phase to the ground is Vcc+Vds (reverse voltage drop of the switch tube), and the winding generates a peak voltage, such as Figure 7 As shown, line a represents the peak voltage value of phase V, which reaches 31V at this time, resulting in the voltage applied to both ends of the switch tube being too high. Therefore, the peak voltage can easily cause insulation damage to the motor winding. At the same time, for the normal operation of the circuit, the requirements for the switch tube also need to be improved. At this time, a switch tube with a withstand voltage of 40V is required, which is more expensive.

[0003] Please refer to the Chinese invention patent application announcement No. CN103618485B published on January 13, 2016, which discloses a method for detecting the initial position of a brushless DC motor without a position sensor. According to the three-phase six-state, the switch tubes are turned on two by two, and the bus current is collected six times. According to the relationship between the currents, a primary positioning is achieved to determine the critical position of the rotor, and the switch tubes are turned on three by three again to achieve a secondary positioning to determine the accurate position of the rotor. This patent uses current to achieve simple rotor positioning, but does not suppress the peak voltage generated when the switch tube changes phase, so it will cause damage to the motor. At the same time, it has high requirements for the selection of the switch tube.

[0004] Therefore, it is necessary to design a new brushless motor positioning system to solve the technical problems existing in the prior art. [Summary of the invention]

[0005] In view of the deficiencies in the prior art, an object of the present invention is to provide a brushless motor current sampling method and a brushless motor control mechanism that can suppress peak voltage.

[0006] The present invention solves the existing technical problems by adopting the following technical solutions: a brushless motor current sampling method, comprising: an inverter circuit and a control circuit connected to the brushless motor, the inverter circuit comprising a positive and negative DC bus, at least two bridge arms, the bridge arms being a first bridge arm and a second bridge arm, the first bridge arm and the second bridge arm being connected between the positive and negative DC bus, and an upper switch tube and a lower switch tube being respectively provided on the first bridge arm and the second bridge arm, and the upper switch tube being connected to the positive DC bus, and the lower switch tube being connected to the negative DC bus, and each lower switch tube being respectively connected in reverse parallel There is a diode, and the control circuit controls the upper and lower switch tubes to be turned on in at least one conduction state and adopts DC bus current values ​​in different states. After the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the second bridge arm to be turned on at the same time for a first predetermined time, the first current value can be collected, and the upper switch tube of the first bridge arm can be turned off, while the lower switch tube of the second bridge arm continues to be turned on. The lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling circuit, and the lower switch tube of the second bridge arm is turned off after being turned on for a second predetermined time.

[0007] A further improvement scheme is: after the control circuit controls the upper switch tube of the second bridge arm and the lower switch tube of the first bridge arm to be turned on at the same time for a first predetermined time, the second current value can be collected, the upper switch tube of the second bridge arm is turned off, and the lower switch tube of the first bridge arm continues to be turned on. The diode connected in parallel with the lower switch tube of the first bridge arm and the lower switch tube of the second bridge arm forms a freewheeling circuit, and the lower switch tube of the first bridge arm is turned off after being turned on for the second predetermined time.

[0008] A further improved solution is: the bridge arm includes a third bridge arm, and an upper switch tube and a lower switch tube are provided on the third bridge arm, the upper switch tube is connected to the positive DC bus, and the lower switch tube is connected to the negative DC bus. After the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the third bridge arm to be turned on at the same time for a first predetermined time, a third current value can be collected, and the upper switch tube of the first bridge arm is turned off, while the lower switch tube of the third bridge arm continues to be turned on, and the lower switch tube of the third bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling circuit, and the lower switch tube of the third bridge arm is turned off after being turned on for a second predetermined time; after the control circuit controls the upper switch tube of the third bridge arm and the lower switch tube of the first bridge arm to be turned on at the same time for a first predetermined time, a fourth current value can be collected, and the upper switch tube of the third bridge arm is turned off, while the lower switch tube of the first bridge arm continues to be turned on, and the lower switch tube of the first bridge arm and the diode connected in parallel with the lower switch tube of the third bridge arm form a freewheeling circuit, and the lower switch tube of the first bridge arm is turned off after being turned on for the second predetermined time.

[0009] A further improvement scheme is: after the control circuit controls the upper switch tube of the second bridge arm and the lower switch tube of the third bridge arm to be turned on at the same time for the first predetermined time, the fifth current value can be collected, and the upper switch tube of the second bridge arm can be turned off, while the lower switch tube of the third bridge arm continues to be turned on, and the lower switch tube of the third bridge arm and the diode connected in parallel with the lower switch tube of the second bridge arm form a freewheeling circuit, and the lower switch tube of the third bridge arm is turned off after being turned on for the second predetermined time; after the control circuit controls the upper switch tube of the third bridge arm and the lower switch tube of the second bridge arm to be turned on at the same time for the first predetermined time, the sixth current value can be collected, and the upper switch tube of the third bridge arm can be turned off, while the lower switch tube of the second bridge arm continues to be turned on, and the lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the third bridge arm form a freewheeling circuit, and the lower switch tube of the second bridge arm is turned off after being turned on for the second predetermined time.

[0010] The present invention can also adopt the following technical solutions to solve the problems of the prior art: a brushless motor control mechanism, comprising: an inverter circuit and a control circuit connected to the brushless motor, the inverter circuit comprising a positive and negative DC bus, and at least two bridge arms, the bridge arms being a first bridge arm and a second bridge arm, the first bridge arm and the second bridge arm being connected between the positive and negative DC bus, and an upper switch tube and a lower switch tube being respectively provided on the first bridge arm and the second bridge arm, and the upper switch tube being connected to the positive DC bus, and the lower switch tube being connected to the negative DC bus, and each lower switch tube being respectively connected to a diode in reverse parallel, and the control circuit The control circuit controls the upper and lower switch tubes to be turned on in at least one conduction state, and adopts DC bus current values ​​in different states, and determines the initial position of the rotor according to the current value. After the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the second bridge arm to be turned on at the same time for a first predetermined time, the first current value can be collected, and the upper switch tube of the first bridge arm can be turned off, while the lower switch tube of the second bridge arm continues to be turned on. The lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling circuit, and the lower switch tube of the second bridge arm is turned off after being turned on for a second predetermined time.

[0011] A further improvement scheme is: the control circuit includes a microprocessor MCU, a MOS drive module, and a current sampling circuit.

[0012] A further improved solution is: the current sampling circuit includes a sampling resistor and a current detection circuit, and the sampling resistor is arranged on the negative DC bus of the inverter circuit.

[0013] A further improved solution is: the microprocessor MCU is connected to a MOS driving module, and the MOS driving module controls the conduction of the switch tubes according to the information of the microprocessor MCU.

[0014] A further improvement is as follows: the microprocessor MCU has a storage unit, the current detection circuit is used to detect the voltage across the sampling resistor to obtain the bus current value, and amplify and transmit it to the microprocessor MCU, and the microprocessor stores the bus current values ​​in different conduction states.

[0015] A further improved solution is: the first predetermined time range is 40us to 200us.

[0016] A further improvement is that the second predetermined time is not less than 160us.

[0017] A further improvement scheme is: after the control circuit controls the upper switch tube of the second bridge arm and the lower switch tube of the first bridge arm to be turned on at the same time for the first predetermined time, the second current value can be collected, and the upper switch tube of the second bridge arm is turned off, while continuing to turn on the lower switch tube of the first bridge arm. The diode connected in parallel with the lower switch tube of the first bridge arm and the lower switch tube of the second bridge arm forms a freewheeling circuit, and the lower switch tube of the first bridge arm is turned off after being turned on for the second predetermined time.

[0018] A further improved solution is: the bridge arm includes a third bridge arm, and the third bridge arm is provided with an upper switch tube and a lower switch tube, the upper switch tube is connected to the positive DC bus, and the lower switch tube is connected to the negative DC bus. After the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the third bridge arm to be turned on at the same time for a first predetermined time, a third current value can be collected, and the upper switch tube of the first bridge arm is turned off, while the lower switch tube of the third bridge arm continues to be turned on, and the lower switch tube of the third bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling circuit, and the lower switch tube of the third bridge arm is turned off after being turned on for a second predetermined time; after the control circuit controls the upper switch tube of the third bridge arm and the lower switch tube of the first bridge arm to be turned on at the same time for a first predetermined time, a fourth current value can be collected, and the upper switch tube of the third bridge arm is turned off, while the lower switch tube of the first bridge arm continues to be turned on, and the lower switch tube of the first bridge arm and the diode connected in parallel with the lower switch tube of the third bridge arm form a freewheeling circuit, and the lower switch tube of the first bridge arm is turned off after being turned on for the second predetermined time.

[0019] A further improvement scheme is: after the control circuit controls the upper switch tube of the second bridge arm and the lower switch tube of the third bridge arm to be turned on at the same time for the first predetermined time, the fifth current value can be collected, and the upper switch tube of the second bridge arm is turned off, while the lower switch tube of the third bridge arm continues to be turned on, the lower switch tube of the third bridge arm and the diode connected in parallel with the lower switch tube of the second bridge arm form a freewheeling circuit, and the lower switch tube of the third bridge arm is turned off after being turned on for the second predetermined time; after the control circuit controls the upper switch tube of the third bridge arm and the lower switch tube of the second bridge arm to be turned on at the same time for the first predetermined time, the sixth current value can be collected, and the upper switch tube of the third bridge arm is turned off, while the lower switch tube of the second bridge arm continues to be turned on, the lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the third bridge arm form a freewheeling circuit, and the lower switch tube of the second bridge arm is turned off after being turned on for the second predetermined time.

[0020] Compared with the prior art, the present invention has the following beneficial effects: the present invention includes an inverter circuit and a control circuit, the inverter circuit includes a positive and negative DC bus, at least two bridge arms, the bridge arms are a first bridge arm and a second bridge arm, the control circuit controls the upper and lower switch tubes of the first bridge arm and the second bridge arm to be turned on in at least one conduction state, and adopts DC bus current values ​​in different states, after the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the second bridge arm to be turned on at the same time for a first predetermined time, the first current value can be collected, the upper switch tube of the first bridge arm is turned off, and the lower switch tube of the second bridge arm continues to be turned on, the lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling circuit, after being turned on for the second predetermined time, the lower switch tube of the second bridge arm is turned off, and the freewheeling direction is changed, so that the peak voltage can be reduced, thereby reducing the voltage applied to both ends of the switch tube, which can reduce the selection requirements of the switch tube and reduce the cost. [Drawings]

[0021] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings:

[0022] Figure 1 It is a schematic diagram of the brushless motor control mechanism of the present invention;

[0023] Figure 2 It is a schematic diagram of the positions of the stator winding and the rotor of the brushless motor of the present invention;

[0024] Figure 3 It is a schematic diagram of the current flow direction when the UV phase of the brushless motor of the present invention is turned on;

[0025] Figure 4 It is a schematic diagram of the current flow direction of the brushless motor freewheeling of the present invention;

[0026] Figure 5 is the voltage waveform of the freewheeling current of the present invention;

[0027] Figure 6It is a schematic diagram of the current flow direction of the freewheeling current in the prior art;

[0028] Figure 7 It is the voltage waveform of the freewheeling in the prior art. [Specific implementation method]

[0029] The present invention is further described in detail below in conjunction with the accompanying drawings and implementation modes.

[0030] See also Figure 1 The figure shows a schematic diagram of the three-phase brushless motor control mechanism of the present invention, which includes a DC power supply, a brushless motor, a three-phase full-bridge inverter circuit and a control circuit. The brushless motor is star-connected, and can also be delta-connected; the three-phase full-bridge inverter circuit inverts the DC power provided by the DC power supply into AC power to supply power to the three-phase winding of the brushless motor; the control circuit includes a microprocessor MCU, a MOS drive module, and a current sampling circuit, and the MOS drive module responds to the control signal received from the microprocessor MCU to drive the opening and closing of the switch tube of the three-phase full-bridge inverter circuit.

[0031] The following is an explanation of the control of the inverter circuit of two bridge arms: the control mechanism of the brushless motor includes an inverter circuit and a control circuit, the inverter circuit includes a positive and negative DC bus, a first bridge arm and a second bridge arm, the first bridge arm and the second bridge arm are connected between the positive and negative DC bus, and the first bridge arm and the second bridge arm are respectively provided with an upper switch tube and a lower switch tube, and the upper switch tube is connected to the positive DC bus, and the lower switch tube is connected to the negative DC bus, each upper and lower switch tube is respectively connected in reverse parallel with a diode, in some structures, the diode is a parasitic diode of a MOS tube or other transistor, and in other structures, the diode is a parasitic diode of a MOS tube or other transistor. In the structure, the diode can be connected in parallel with other switch tubes, and the control circuit controls the upper and lower switch tubes to be turned on in at least one conduction state and adopts DC bus current values ​​in different states. After the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the second bridge arm to be turned on at the same time for a first predetermined time, the first current value can be collected, the upper switch tube of the first bridge arm is turned off, and the lower switch tube of the second bridge arm continues to be turned on. The lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling circuit, and the lower switch tube of the second bridge arm is turned off after being turned on for the second predetermined time.

[0032] See also Figure 1As shown, in this embodiment, the inverter circuit is composed of three bridge arms, including positive and negative DC bus bars, a first bridge arm, a second bridge arm, and a third bridge arm, each bridge arm is connected between the positive and negative DC bus bars, the first bridge arm is composed of a first switch tube Q1 (also called an upper switch) and a fourth switch tube Q4 (also called a lower switch) connected in series; the second bridge arm is composed of a second switch tube Q2 (also called an upper switch) and a fifth switch tube Q5 (also called a lower switch) connected in series; the third bridge arm is composed of a third switch tube Q3 (also called an upper switch) and a sixth switch tube Q6 (also called a lower switch) connected in series, and each upper and lower switch tube is respectively connected in reverse parallel with diodes D1 to D6; the brushless motor includes a first phase U, a second phase V and a third phase W, one end of the three-phase winding is connected to a point, the other end of the first phase U is connected to the midpoint of the first bridge arm, the other end of the second phase V is connected to the midpoint of the second bridge arm, and the other end of the third phase W is connected to the midpoint of the third bridge arm.

[0033] The control circuit includes a microprocessor MCU, a MOS drive module, and a current sampling circuit. The sampling circuit includes a sampling resistor R1 arranged on the negative DC bus, and a current detection circuit connected to both ends of the sampling resistor R1. The voltage across the sampling resistor R1 is detected to obtain the current flowing through the bus, and the bus current is amplified and transmitted to the microprocessor MCU. The microprocessor MCU adopts a three-phase six-state two-by-two conduction method. Each state is that the upper switch tube of one bridge arm and the lower switch tube of any other bridge arm are turned on in pairs. The upper and lower switch tubes of the same bridge arm cannot be turned on at the same time. Therefore, the inverter circuit can control the switch tube to be turned on in the following six states: Q1Q5 is turned on, Q1Q6 is turned on, Q2Q4 is turned on, Q2Q6 is turned on, Q3Q4 is turned on, and Q3Q5 is turned on. The motor is switched by switching between six states. Please refer to Figure 2As shown, it is a schematic diagram of the stator winding structure and rotor position of the motor. The stator winding structure forms 6 sectors, each sector corresponds to the position area where the rotor is located, and each position area corresponds to every two switch tubes being turned on. At the time of initial positioning, the microprocessor MCU controls the MOS drive module to turn on the UV two-phase (Q1, Q5 are turned on), the microprocessor MCU samples the bus current once, and turns on the VU two-phase (Q2, Q4 are turned on), UW two-phase (Q1, Q6 are turned on), WU two-phase (Q3, Q4 are turned on), VW two-phase (Q2, Q6 are turned on), WV two-phase (Q3, Q5 are turned on) in turn according to the above method, and samples the bus current values ​​Iuv, Ivu, Iuw, Iwu, Ivw, Iwu respectively. The microprocessor MCU The sampled bus current value calculates the positive and negative current difference △I1=|Iuv-Ivu|, △I2=|Iuw-Iwu|, △I3=|Ivw-Iwv| flowing through each two-phase winding, and compares the six bus current values ​​and the three positive and negative current differences with the relationship between the current and the initial position of the rotor stored in the internal memory of the microprocessor MCU (refer to Table 1), determines the initial position of the rotor, and after obtaining the position, refers to the working switch tube to be opened corresponding to the initial position of the rotor stored in the microprocessor MCU (refer to Table 2), such as Figure 2 As shown, if the initial position of the rotor is position 1, the microprocessor MCU controls the MOS driver module to first turn on the switch tube Q1Q5, and then cyclically turn on in the order of Q1Q5, Q1Q6, Q2Q6, Q2Q4, Q3Q4, and Q3Q5 to make the rotor rotate counterclockwise. If it needs to rotate clockwise, it is cyclically turned on in the reverse order as described above; if the initial position of the rotor is position 2, the microprocessor MCU controls the MOS driver module to first turn on the switch tube Q1Q6, and then cyclically turn on in the order of Q1Q6, Q2Q6, Q2Q4, Q3Q4, Q3Q5, and Q1Q5 to make the rotor rotate counterclockwise. If it needs to rotate clockwise, it is cyclically turned on in the reverse order as described above; when different initial positions of the rotor are detected, the switch tube corresponding to the rotor position is first turned on according to Table 2, and is turned on in the above cyclic order. During the rotation process, the back electromotive force zero crossing point is detected by the back electromotive force detection circuit to determine the rotor position and control the commutation of the rotor.

[0034] Table 1 shows the relationship between each bus current and the rotor position.

[0035]

[0036] Table 2 shows the working switch tubes that need to be opened corresponding to the positions of each rotor.

[0037] Initial position of the rotor Working switch tube Position 1 Q1, Q5 Position 2 Q1, Q6 Location 3 Q2, Q6 Position 4 Q2, Q4 Location 5 Q3, Q4 Position 6 Q3, Q5

[0038] When sampling the current, the switch tubes Q1Q5, Q2Q4, Q1Q6, Q3Q4, Q2Q6, and Q3Q5 need to be turned on in sequence. Figure 3 As shown, it is a schematic diagram of the current flow when the UV phase of the brushless motor of the present invention is turned on. The switch tube Q1Q5 is turned on, and the current flows into the ground wire through the positive electrode BAT+ of the power supply, the switch tube Q1, the U phase winding, the V phase winding, and the switch tube Q5. After the switch tube Q1Q5 is turned on for a period of time, the microprocessor MCU can sample the bus current Iuv. After sampling the current, the switch tube Q1Q5 needs to be disconnected, and the switch tube Q2Q4 is switched on to sample the bus current Ivu. Figure 4 As shown in FIG. 1 , the current flow direction of the freewheeling in this embodiment is shown. After the microprocessor MCU controls Q1Q5 to be turned on for the first predetermined time of 180us, the upper switch tube Q1 is turned off first, and the lower switch tube Q5 is kept turned on for a delay of 180us. At this time, because the current of the UV phase winding cannot change suddenly, the current forms a loop through the diode D4, the U phase winding, the V phase winding, and the switch tube Q5 to achieve freewheeling. After the current is consumed, the switch tube Q5 is turned off. At this time, the peak voltage value of the V phase is as follows: Figure 5 As shown at line a, the peak voltage value is reduced to 26.6 V. Then, according to the above-mentioned freewheeling mode, the switch tubes Q2Q4, Q1Q6, Q3Q4, Q2Q6, and Q3Q5 are continuously turned on, that is, while sampling the six bus currents, the peak voltage can be reduced, and the voltage applied to both ends of the switch tube is reduced to 26.6 V. A switch tube with a withstand voltage of 30 V can be selected, which can ensure the normal operation of the circuit and save costs.

[0039] When the two switch tubes in each state are switched on, the control mechanism of the present invention first disconnects the upper switch tube and delays the switching on of the lower switch tube, so that the diode connected in parallel with the lower switch tube of the bridge arm corresponding to the upper switch tube in this state, the corresponding winding and the lower switch tube in this state form a freewheeling loop, thereby reducing the peak voltage and lowering the terminal voltage of the switch tube. Depending on the circuit, this structure can reduce the peak voltage more. Therefore, the requirements for the switch tube can be reduced, a switch tube with a lower withstand voltage can be selected, and costs can be saved.

[0040] The present invention also provides a brushless motor current sampling method, and the microprocessor MCU controls the MOS driving module to turn on UV two phases (Q1 and Q5 are turned on), VU two phases (Q2 and Q4 are turned on), UW two phases (Q1 and Q6 are turned on), WU two phases (Q3 and Q4 are turned on), VW two phases (Q2 and Q6 are turned on), and WV two phases (Q3 and Q5 are turned on), and respectively samples the bus current values ​​Iuv, Ivu, Iuw, Iwu, Ivw, and Iwv.The microprocessor controls the switch tubes Q1Q5 to be turned on. After the switch tubes Q1Q5 are turned on for the first predetermined time of 180us, the bus current Iuv is sampled. After the current Iuv is sampled, the upper switch tube Q1 is turned off first, and the lower switch tube Q5 is kept turned on for a delay of 180us. At this time, because the current of the UV phase winding cannot change suddenly, the current forms a loop through the diode D4, the U phase winding, the V phase winding, and the switch tube Q5 to achieve continuous flow. After the current is consumed, the switch tube Q5 is turned off. The microprocessor controls the switch tubes Q2Q4 to be turned on. After the switch tubes Q2Q4 are turned on for the first predetermined time of 180us, the bus current Ivu is sampled. After the current Ivu is sampled, the upper switch tube Q1 is turned off first. The switch tube Q2 is controlled to delay the conduction of the lower switch tube Q4 for 180us. At this time, the current forms a loop through the diode D5, the V-phase winding, the U-phase winding, and the switch tube Q4 to achieve freewheeling. After the current is consumed, the switch tube Q4 is turned off. The microprocessor controls the switch tubes Q1Q6 to turn on. After the switch tubes Q1Q6 are turned on for the first predetermined time of 180us, the bus current Iuw is sampled. After the current Iuw is sampled, the upper switch tube Q1 is turned off first, and the lower switch tube Q6 is kept on for 180us. At this time, the current forms a loop through the diode D4, the U-phase winding, the W-phase winding, and the switch tube Q6 to achieve freewheeling. After the current is consumed, the switch tube Q6 is turned off. The microprocessor The processor controls the switch tube Q3Q4 to be turned on. After the switch tube Q3Q4 is turned on for the first predetermined time of 180us, the bus current Iwu is sampled. After the current Iwu is sampled, the upper switch tube Q3 is turned off first, and the lower switch tube Q4 is kept turned on for a delay of 180us. At this time, the current forms a loop through the diode D6, the W phase winding, the U phase winding, and the switch tube Q4 to achieve freewheeling. After the current is consumed, the switch tube Q4 is turned off. The microprocessor controls the switch tube Q2Q6 to be turned on. After the switch tube Q2Q6 is turned on for the first predetermined time of 180us, the bus current Ivw is sampled. After the current Ivw is sampled, the upper switch tube Q2 is turned off first, and the lower switch tube Q6 is kept turned on for a delay of The microprocessor controls the switch tube Q3Q5 to conduct. After the switch tube Q3Q5 is conducted for the first predetermined time of 180us, the bus current Iwv is sampled. After the current Iwv is sampled, the upper switch tube Q3 is first turned off, and the lower switch tube Q5 is kept on for 180us. At this time, the current forms a loop through the diode D6, the W phase winding, the V phase winding, and the switch tube Q5 to achieve freewheeling. After the current is consumed, the switch tube Q5 is turned off, and the 6 bus current values ​​of the brushless motor can be sampled. Reduce the peak voltage, lower the terminal voltage of the switch tube, and improve the safety of the circuit.

[0041] The brushless motor current sampling method of the present invention disconnects the upper switch tube first and delays the switching on of the lower switch tube when the two switch tubes in each state are switched on, so that the diode connected in parallel with the lower switch tube of the bridge arm corresponding to the upper switch tube in this state, the corresponding winding and the lower switch tube in this state form a freewheeling loop, thereby reducing the peak voltage and lowering the terminal voltage of the switch tube. Depending on the circuit, this structure can reduce the peak voltage more, therefore, the requirements for the switch tube can be reduced, a switch tube with a lower withstand voltage can be selected, and costs can be saved.

[0042] The present invention is not limited to the above specific implementations. A person skilled in the art can easily understand that there are many other alternatives to the brushless motor current sampling method and control mechanism of the present invention without departing from the principle and scope of the present invention. The protection scope of the present invention shall be subject to the content of the claims.

Claims

1. A brushless motor current sampling method, comprising: An inverter circuit and a control circuit connected to a brushless motor, wherein the inverter circuit includes a positive and negative DC bus and at least two bridge arms, wherein the bridge arms are a first bridge arm and a second bridge arm, wherein the first bridge arm and the second bridge arm are connected between the positive and negative DC bus, and an upper switch tube and a lower switch tube are respectively provided on the first bridge arm and the second bridge arm, wherein the upper switch tube is connected to the positive DC bus, and the lower switch tube is connected to the negative DC bus, and each lower switch tube is respectively connected in reverse parallel with a diode, wherein the control circuit controls the upper and lower switch tubes to be turned on in at least one conduction state, and collects DC bus current values ​​in different states; wherein the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the second bridge arm to simultaneously turn on the first After a predetermined time, the first current value is collected, and the upper switch tube of the first bridge arm is turned off, while the lower switch tube of the second bridge arm continues to be turned on, and the lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling circuit, and the lower switch tube of the second bridge arm is turned off after being turned on for a second predetermined time; after the control circuit controls the upper switch tube of the second bridge arm and the lower switch tube of the first bridge arm to be turned on at the same time for a first predetermined time, the second current value is collected, and the upper switch tube of the second bridge arm is turned off, while the lower switch tube of the first bridge arm continues to be turned on, and the lower switch tube of the first bridge arm and the diode connected in parallel with the lower switch tube of the second bridge arm form a freewheeling circuit, and the lower switch tube of the first bridge arm is turned off after being turned on for the second predetermined time.

2. The brushless motor current sampling method according to claim 1, characterized in that: The bridge arm includes a third bridge arm, on which an upper switch tube and a lower switch tube are provided, the upper switch tube is connected to the positive DC bus, and the lower switch tube is connected to the negative DC bus. After the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the third bridge arm to be turned on simultaneously for a first predetermined time, a third current value is collected, and the upper switch tube of the first bridge arm is turned off, while the lower switch tube of the third bridge arm is continued to be turned on. The lower switch tube of the third bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling loop, and the lower switch tube of the third bridge arm is turned off after being turned on for a second predetermined time; after the control circuit controls the upper switch tube of the third bridge arm and the lower switch tube of the first bridge arm to be turned on simultaneously for a first predetermined time, a fourth current value is collected, and the upper switch tube of the third bridge arm is turned off, while the lower switch tube of the first bridge arm is continued to be turned on. The lower switch tube of the first bridge arm and the diode connected in parallel with the lower switch tube of the third bridge arm form a freewheeling loop, and the lower switch tube of the first bridge arm is turned off after being turned on for the second predetermined time.

3. The brushless motor current sampling method according to claim 2, characterized in that: After the control circuit controls the upper switch tube of the second bridge arm and the lower switch tube of the third bridge arm to be turned on simultaneously for the first predetermined time, the fifth current value is collected, and the upper switch tube of the second bridge arm is turned off, while the lower switch tube of the third bridge arm continues to be turned on, and the lower switch tube of the third bridge arm and the diode connected in parallel with the lower switch tube of the second bridge arm form a freewheeling circuit, and the lower switch tube of the third bridge arm is turned off after being turned on for the second predetermined time; after the control circuit controls the upper switch tube of the third bridge arm and the lower switch tube of the second bridge arm to be turned on simultaneously for the first predetermined time, the sixth current value is collected, and the upper switch tube of the third bridge arm is turned off, while the lower switch tube of the second bridge arm continues to be turned on, and the lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the third bridge arm form a freewheeling circuit, and the lower switch tube of the second bridge arm is turned off after being turned on for the second predetermined time.

4. A brushless motor control mechanism, comprising: An inverter circuit and a control circuit connected to a brushless motor, wherein the inverter circuit includes a positive and negative DC bus and at least two bridge arms, wherein the bridge arms are a first bridge arm and a second bridge arm, wherein the first bridge arm and the second bridge arm are connected between the positive and negative DC bus, and an upper switch tube and a lower switch tube are respectively provided on the first bridge arm and the second bridge arm, wherein the upper switch tube is connected to the positive DC bus, and the lower switch tube is connected to the negative DC bus, and each lower switch tube is respectively connected in reverse parallel with a diode, wherein the control circuit controls the upper and lower switch tubes to be turned on in at least one conduction state, and collects DC bus current values ​​in different states, and determines the initial position of the rotor according to the current value; wherein the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the second bridge arm to be turned on simultaneously for a first predetermined time, and collects The control circuit controls the upper switch tube of the second bridge arm and the lower switch tube of the first bridge arm to be turned on simultaneously for the first predetermined time, collects the second current value, turns off the upper switch tube of the second bridge arm, and continues to turn on the lower switch tube of the first bridge arm. The lower switch tube of the first bridge arm and the diode connected in parallel with the lower switch tube of the second bridge arm form a freewheeling circuit. After being turned on for the second predetermined time, the lower switch tube of the second bridge arm is turned off. The bridge arm includes a third bridge arm, on which an upper switch tube and a lower switch tube are provided.

5. The brushless motor control mechanism according to claim 4, characterized in that: The control circuit comprises a microprocessor MCU, a MOS driving module and a current sampling circuit.

6. The brushless motor control mechanism according to claim 5, characterized in that: The current sampling circuit comprises a sampling resistor and a current detection circuit, and the sampling resistor is arranged on the negative DC bus of the inverter circuit.

7. The brushless motor control mechanism according to claim 5, characterized in that: The microprocessor MCU is connected to a MOS driving module, and the MOS driving module controls the conduction of the switch tubes according to information from the microprocessor MCU.

8. The brushless motor control mechanism according to claim 6 or 7, characterized in that: The current sampling circuit includes a sampling resistor and a current detection circuit; the microprocessor MCU has a storage unit, and the current detection circuit is used to detect the voltage across the sampling resistor to obtain the bus current value, and amplify and transmit it to the microprocessor MCU, and the microprocessor stores the bus current values ​​in different conduction states.

9. The brushless motor control mechanism according to claim 4, characterized in that: The first predetermined time range is from 40us to 200us.

10. The brushless motor control mechanism according to claim 4, characterized in that: The second predetermined time is not less than 160 us.

11. The brushless motor control mechanism according to claim 4, characterized in that: The upper switch tube is connected to the positive DC bus, and the lower switch tube is connected to the negative DC bus. After the control circuit controls the upper switch tube of the first bridge arm and the lower switch tube of the third bridge arm to be turned on at the same time for a first predetermined time, a third current value is collected, and the upper switch tube of the first bridge arm is turned off, while the lower switch tube of the third bridge arm continues to be turned on. The lower switch tube of the third bridge arm and the diode connected in parallel with the lower switch tube of the first bridge arm form a freewheeling loop, and the lower switch tube of the third bridge arm is turned off after being turned on for a second predetermined time; after the control circuit controls the upper switch tube of the third bridge arm and the lower switch tube of the first bridge arm to be turned on at the same time for a first predetermined time, a fourth current value is collected, and the upper switch tube of the third bridge arm is turned off, while the lower switch tube of the first bridge arm continues to be turned on. The lower switch tube of the first bridge arm and the diode connected in parallel with the lower switch tube of the third bridge arm form a freewheeling loop, and the lower switch tube of the first bridge arm is turned off after being turned on for the second predetermined time.

12. The brushless motor control mechanism according to claim 4 or 11, characterized in that: After the control circuit controls the upper switch tube of the second bridge arm and the lower switch tube of the third bridge arm to be turned on simultaneously for the first predetermined time, the fifth current value is collected, and the upper switch tube of the second bridge arm is turned off, while the lower switch tube of the third bridge arm continues to be turned on, and the lower switch tube of the third bridge arm and the diode connected in parallel with the lower switch tube of the second bridge arm form a freewheeling circuit, and the lower switch tube of the third bridge arm is turned off after being turned on for the second predetermined time; after the control circuit controls the upper switch tube of the third bridge arm and the lower switch tube of the second bridge arm to be turned on simultaneously for the first predetermined time, the sixth current value is collected, and the upper switch tube of the third bridge arm is turned off, while the lower switch tube of the second bridge arm continues to be turned on, and the lower switch tube of the second bridge arm and the diode connected in parallel with the lower switch tube of the third bridge arm form a freewheeling circuit, and the lower switch tube of the second bridge arm is turned off after being turned on for the second predetermined time.

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