A method for managing stalled-rotor current of a brushless DC motor

Abstract

The present invention discloses a method for managing a brushless DC motor stall current, which belongs to the technical field of motor control. The method comprises the following steps: step S1, real-time monitoring of the motor speed, judging whether the motor speed is the stall speed, if the motor speed is the stall speed, the motor stalls; if the motor speed is not the stall speed, step S2 is entered; step S2, stall detection of the motor is performed, judging whether the motor has a stall trend; step S3, after detecting that the motor has a stall trend, stall current management is intervened, and based on the current phase current peak value and the current electrical angle of the motor, the U-phase current, the V-phase current and the W-phase current of the motor are convergently controlled. The present invention provides a method for managing a brushless DC motor stall current, which manages the stall current when the motor is stalled, and can avoid the problem of damage to power devices due to the overall temperature increase caused by the stall.

Description

Technical Field

[0001] The invention relates to a brushless DC motor stall current management method, belonging to the technical field of motor control. Background Art

[0002] At present, in air-conditioning applications, as the fan motor power of the integrated machine continues to increase, the corresponding electronic hardware power must also be increased. In order to ensure product reliability, the power of the power device has to be increased.

[0003] The fan motor of the integrated machine uses a brushless DC motor. The heat generated by the brushless DC motor when it is stalled is huge, which can easily cause damage to the device. When it is stalled (such as the load is too large to start), the motor does not rotate, and the loss of the controller is mainly divided into switching loss and conduction loss. The switching loss is closely related to the switching frequency, and the conduction loss is closely related to the square of the current. When the integrated machine is stalled, the heat generated by the power device itself causes the temperature of the power device to rise rapidly. The consequence of the temperature increase is that the overcurrent capacity of the crystal source inside the power device decreases, which can easily cause damage to the power device at the same temperature. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a brushless DC motor stall current management method, which manages the stall current when the motor stalls and avoids the problem of power device damage caused by the overall temperature increase caused by the stall.

[0005] In order to solve the above technical problems, the technical solution of the present invention is:

[0006] A brushless DC motor stall current management method, comprising the following steps:

[0007] Step S1, monitor the motor speed in real time to determine whether the motor speed is the stall speed. If the motor speed is the stall speed, the motor stops; if the motor speed is not the stall speed, enter step S2;

[0008] Step S2, performing a stall detection on the motor to determine whether the motor has a stall tendency;

[0009] Step S3: After detecting that the motor is stalling, the stall current management is implemented, and based on the current phase current peak value and the current electrical angle of the motor, the U-phase current, V-phase current and W-phase current of the motor are converged and controlled.

[0010] Furthermore, in step S3, after the stall current management is implemented, the motor speed is monitored in real time to determine whether the motor speed is the stall speed. If the motor speed is the stall speed, the motor stops and the stall current management is terminated.

[0011] Further, in step S2, the motor is subjected to a stall detection to determine whether the motor has a stall tendency, which specifically includes the following steps:

[0012] Step S21, dividing the motor into sectors;

[0013] Step S22: Set a timer, which is used to measure the time consumed by the basic voltage vector passing through each sector, and obtain the time consumed by the basic voltage vector passing through each sector. t ;

[0014] Step S23: The time S consumed by the basic voltage vector passing through each sector t The time threshold B consumed by the basic voltage vector passing through each sector is t For comparison, if S t >B t , it is determined that the basic voltage vector has timed out in the current sector and the motor has a tendency to stall.

[0015] Furthermore, in step S21, the sectors of the motor are divided, which specifically includes the following steps:

[0016] Coordinate system conversion;

[0017] Divide the motor into 6 sectors and determine the sector where the voltage space vector Uout is located;

[0018] Determine the sector number.

[0019] Furthermore, the coordinate system conversion specifically includes the following steps:

[0020] First, the three-phase current of the motor , , The current in the two-phase stationary coordinate system α-β is obtained by Clarke transformation , ;

[0021] Then, , After Park transformation, the current in the synchronous rotating coordinate system dq is obtained , .

[0022] Further, the sectors of the motor are divided into 6 sectors, and the sector where the voltage space vector Uout is located is determined, specifically including the following steps:

[0023] The sectors of the motor are divided into 6 sectors, namely the first sector, the second sector, the third sector, the fourth sector, the fifth sector and the sixth sector;

[0024] The components of the voltage space vector Uout in the α-β coordinate system are expressed as uα and uβ, and each sector corresponds to a positive and negative combination of uα and uβ;

[0025] According to the positive and negative relationship between uα and uβ, the sector where the voltage space vector Uout is located is determined.

[0026] Furthermore, the calculation method of the basic voltage vector is as follows:

[0027] After determining the sector where the voltage space vector Uout is located, the basic voltage vector and the action time of the basic voltage vector required to synthesize the vector are calculated according to the SVPWM algorithm.

[0028] Furthermore, in step S3, the motor is intervened in the stall current management, specifically including the following steps:

[0029] Based on the current phase current peak value and the current electrical angle of the motor, the U-phase current, V-phase current and W-phase current of the motor are converged and controlled.

[0030] Furthermore, the calculation formula for performing convergence control on the U-phase current of the motor is as follows:

[0031] ;

[0032] in, is the U-phase current after being controlled; θ is the electrical angle of the motor at this time; is the peak phase current; , , is the proportionality coefficient, 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter; t is the time parameter.

[0033] Furthermore, the calculation formula for performing convergence control on the V-phase current of the motor is as follows:

[0034] ;

[0035] in, is the V-phase current after being controlled; θ is the electrical angle of the motor at this time; is the peak phase current; , , is the proportionality coefficient, 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter; t is the time parameter.

[0036] Furthermore, the calculation formula for performing convergence control on the W-phase current of the motor is as follows:

[0037] ;

[0038] in, is the W-phase current after being controlled; θ is the electrical angle of the motor at this time; is the peak phase current; , , is the proportionality coefficient, 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter; t is the time parameter.

[0039] By adopting the above technical solution, the present invention changes the stall detection method from the original motor running state change within the rated time as the basis for stall judgment, to adding a method of judging whether the basic voltage vector has timed out in the current sector. Then, the method of managing the stall current is used to optimize the stall operation heating condition, so that the crystal source temperature of the power device is kept at a relatively low temperature (the upper limit of the current allowed to pass at a relatively low temperature is greater than the upper limit of the current allowed to pass at a high temperature), ensuring the safety of the power device. Without changing the power of the hardware power device, the stall current management method is used to manage the stall current, which can reduce the risk of heat damage caused by stalling, and effectively reduce product costs while ensuring quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A flow chart of a brushless DC motor stall current management method of the present invention;

[0041] Figure 2 It is a current waveform diagram of the motor of the present invention when it goes from normal operation to stall;

[0042] Figure 3 This is a current waveform diagram after adding the locked-rotor current management of the present invention. DETAILED DESCRIPTION

[0043] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0044] like Figure 1 As shown, this embodiment provides a brushless DC motor stall current management method, which includes the following steps:

[0045] Step S1, monitor the motor speed in real time to determine whether the motor speed is the stall speed. If the motor speed is the stall speed, the motor stops; if the motor speed is not the stall speed, enter step S2.

[0046] Step S2, performing a stall detection on the motor to determine whether the motor has a stall tendency, specifically comprising the following steps:

[0047] Step S21, dividing the motor into sectors;

[0048] Step S22: Set a timer, which is used to measure the time consumed by the basic voltage vector passing through each sector, and obtain the time consumed by the basic voltage vector passing through each sector. t ;

[0049] Step S23: The time S consumed by the basic voltage vector passing through each sector t The time threshold B consumed by the basic voltage vector passing through each sector is t For comparison, if S t >B t , it is determined that the basic voltage vector has timed out in the current sector and the motor has a tendency to stall.

[0050] Wherein, in step S21, the sectors of the motor are divided, which specifically includes the following steps:

[0051] 1. Coordinate system conversion:

[0052] First, the three-phase current of the motor , , The current in the two-phase stationary coordinate system α-β is obtained by Clarke transformation , ;

[0053] Then, , After Park transformation, the current in the synchronous rotating coordinate system dq is obtained , In this sector division process, the main focus is on the current or voltage component in the α-β coordinate system.

[0054] 2. Divide the motor into 6 sectors and determine the sector where the voltage space vector Uout is located:

[0055] Dividing the sectors of the motor into a first sector, a second sector, a third sector, a fourth sector, a fifth sector and a sixth sector;

[0056] The components of the voltage space vector Uout in the α-β coordinate system are expressed as uα and uβ, and each sector corresponds to a specific positive and negative combination of uα and uβ;

[0057] According to the positive and negative relationship between uα and uβ, the sector where the voltage space vector Uout is located can be determined;

[0058] In the first sector, uα > 0 and uβ ≥ 0. At this time, the voltage space vector Uout is located in the first quadrant and is closer to the α axis.

[0059] In the second sector, when |uβ / uα|≥√3 and uβ > 0 are the conditions, the voltage space vector Uout is located in the first quadrant, but is farther away from the α-axis and closer to the β-axis.

[0060] In the third sector, uα < 0 and uβ ≥ 0. At this time, the voltage space vector Uout is located in the second quadrant and is closer to the β axis.

[0061] In the fourth sector, uα < 0 and uβ < 0. At this time, the voltage space vector Uout is located in the third quadrant and is closer to the negative direction of the α axis.

[0062] In the fifth sector, when |uβ / uα|≥√3 and uβ < 0 are the conditions, the voltage space vector Uout is located in the third quadrant, but is further away from the α-axis and closer to the negative direction of the β-axis.

[0063] In the sixth sector, uα > 0 and uβ ≤ 0. At this time, the voltage space vector Uout is located in the fourth quadrant and is closer to the negative direction of the β axis.

[0064] After determining the sector where the voltage space vector Uout is located, the basic voltage vector and the action time of the basic voltage vector required to synthesize the vector can be calculated according to the SVPWM algorithm.

[0065] 3. Determine the sector number:

[0066] To facilitate subsequent calculations and control, each sector is usually assigned a number (such as 1, 2, 3, 4, 5, 6).

[0067] Step S3: After detecting that the motor is stalling, the stall current management is implemented. Based on the current phase current peak value and the current electrical angle of the motor, the U-phase current, V-phase current and W-phase current of the motor are converged and controlled. After the stall current management is implemented, the motor speed is monitored in real time to determine whether the motor speed is the stall speed. If the motor speed is the stall speed, the motor stops and the stall current management is terminated. The stall current management is specifically as follows:

[0068] The calculation formula for convergence control of the U-phase current of the motor is as follows:

[0069] ;

[0070] in, is the U-phase current after being controlled; θ is the angle at this time (the electrical angle of the motor); is the peak phase current; , , is the proportionality coefficient (obtained from engineering practice based on hardware characteristics), 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter (i.e. the total time from the start of the stall current management to the end of the stall current management); t is the time parameter (the arbitrary time when the stall current management starts is t).

[0071] The calculation formula for convergence control of the V-phase current of the motor is as follows:

[0072] ;

[0073] in, is the V-phase current after being controlled; θ is the angle at this time (the electrical angle of the motor); is the peak phase current; , , is the proportionality coefficient (obtained from engineering practice based on hardware characteristics), 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter (i.e. the total time from the start of the stall current management to the end of the stall current management); t is the time parameter (the arbitrary time when the stall current management starts is t).

[0074] The calculation formula for convergence control of the W-phase current of the motor is as follows:

[0075] ;

[0076] in, is the W-phase current after being controlled; θ is the angle at this time (the electrical angle of the motor); is the peak phase current; , , is the proportionality coefficient (obtained from engineering practice based on hardware characteristics), 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter (i.e. the total time from the start of the stall current management to the end of the stall current management); t is the time parameter (the arbitrary time when the stall current management starts is t).

[0077] The working principle of the present invention is as follows:

[0078] When the motor is running, because each phase is 120 degrees apart, the three-phase current , , The current formula is as follows:

[0079] ;

[0080] ;

[0081] ;

[0082] in, , , is the current corresponding to UVW, is the peak phase current, ω is the angular velocity, and t is the time.

[0083] like Figure 2 As shown in the figure, when the motor is stalled, the angle remains fixed and the current changes from AC to DC. Figure 1 The vertical coordinate is relative to Current proportional parameters, such as Figure 2 It can be found that the current waveform changes from AC to DC, and the current is mainly concentrated on the remaining two phases, which increases the load on the local area of ​​the power device and the corresponding phase line of the motor.

[0084] At this time, the load can be effectively reduced by managing the stall current, that is, using the motor's own controller to control the convergence of the three-phase current. The controlled current formula is as follows:

[0085] ;

[0086] ;

[0087] .

[0088] This embodiment only is equal to 0.05, is equal to 0.95, For example, if it is equal to 0, the current waveform after the locked-rotor current management becomes as follows Figure 3 As shown. Figure 3 It can be seen that although the current becomes direct current when the motor is stalled, it is in a convergent form, especially before the motor stops. As the current converges and decreases, the load on the power devices and motor windings under long-term power-on is greatly reduced.

[0089] The specific embodiments described above further illustrate the technical problems, technical solutions and beneficial effects solved by the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A brushless DC motor stall current management method, characterized in that: It includes the following steps: Step S1, monitor the motor speed in real time to determine whether the motor speed is the stall speed. If the motor speed is the stall speed, the motor stops; if the motor speed is not the stall speed, enter step S2; Step S2, performing a stall detection on the motor to determine whether the motor has a stall tendency; Step S3: after detecting that the motor is stalling, the stall current management is intervened, and based on the current phase current peak value and the current electrical angle of the motor, the U-phase current, the V-phase current and the W-phase current of the motor are converged and controlled; The calculation formula for performing convergence control on the U-phase current of the motor is as follows: ； in, is the U-phase current after being controlled; θ is the electrical angle of the motor at this time; is the peak phase current; , , is the proportionality coefficient, 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter; t is the time parameter; The calculation formula for performing convergence control on the V-phase current of the motor is as follows: ； in, is the V-phase current after being controlled; θ is the electrical angle of the motor at this time; is the peak phase current; , , is the proportionality coefficient, 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter; t is the time parameter; The calculation formula for performing convergence control on the W-phase current of the motor is as follows: ； in, is the W-phase current after being controlled; θ is the electrical angle of the motor at this time; is the peak phase current; , , is the proportionality coefficient, 0≤ <1,0≤ <1,0≤ <1, and <1; is the peak value of the time parameter; t is the time parameter.

2. The brushless DC motor stall current management method according to claim 1, characterized in that: In step S3, after the stall current management is implemented, the motor speed is monitored in real time to determine whether the motor speed is the stall speed. If the motor speed is the stall speed, the motor stops and the stall current management is terminated.

3. The brushless DC motor stall current management method according to claim 1, characterized in that: In step S2, the motor is subjected to a stall detection to determine whether the motor has a stall tendency, which specifically includes the following steps: Step S21, dividing the sectors of the motor; Step S22: Set a timer, which is used to measure the time consumed by the basic voltage vector passing through each sector, and obtain the time consumed by the basic voltage vector passing through each sector. t ; Step S23: The time S consumed by the basic voltage vector passing through each sector t The time threshold B consumed by the basic voltage vector passing through each sector is t For comparison, if S t >B t , it is determined that the basic voltage vector has timed out in the current sector and the motor has a tendency to stall.

4. The brushless DC motor stall current management method according to claim 3, characterized in that: In step S21, the sectors of the motor are divided, which specifically includes the following steps: Coordinate system conversion; Divide the motor into 6 sectors and determine the sector where the voltage space vector Uout is located; Determine the sector number.

5. The brushless DC motor stall current management method according to claim 4, characterized in that: The coordinate system conversion specifically includes the following steps: First, the three-phase current of the motor , , The current in the two-phase stationary coordinate system α-β is obtained by Clarke transformation , ; Then, , After Park transformation, the current in the synchronous rotating coordinate system dq is obtained , .

6. The brushless DC motor stall current management method according to claim 5, characterized in that: The step of dividing the motor sectors into six sectors and determining the sector where the voltage space vector Uout is located specifically includes the following steps: The sectors of the motor are divided into 6 sectors, namely the first sector, the second sector, the third sector, the fourth sector, the fifth sector and the sixth sector; The components of the voltage space vector Uout in the α-β coordinate system are expressed as uα and uβ, and each sector corresponds to a positive and negative combination of uα and uβ; According to the positive and negative relationship between uα and uβ, the sector where the voltage space vector Uout is located is determined.

7. The brushless DC motor stall current management method according to claim 4, characterized in that: The calculation method of the basic voltage vector is as follows: After determining the sector where the voltage space vector Uout is located, the basic voltage vector and the action time of the basic voltage vector required to synthesize the vector are calculated according to the SVPWM algorithm.

Images