Motor phase current reconstruction method

Abstract

The invention relates to the field of electrical engineering and automation, and discloses a motor phase current reconstruction method, which comprises the following steps of: determining an ADC current sampling point of a next period according to the sequence of current three paths of lower bridge PWM (Pulse Width Modulation) triggering, the value of a trigger counter and the time of a minimum sampling window; current sampling is carried out according to the ADC current sampling point of the next period, whether the phase current of the motor can be obtained through direct sampling of a resistor of a lower bridge or not is judged, and if the phase current of the motor cannot be obtained through direct sampling, phase current reconstruction is carried out; and based on the ADC current sampling point of the next period, calculating the delay amount of the motor estimation position, and superposing the delay amount as a time delay component to the motor rotor angle estimated in the next period to obtain the compensated motor rotor angle. According to the invention, the problem that real current signals cannot be sampled due to switching noise at the switching critical moment of PWM of other phases when current of a certain phase is sampled because the three-phase lower bridge PWM turn-on time is short under a high modulation rate is solved.

Description

Technical Field

[0001] The present invention relates to the fields of electrical engineering and automation, and in particular to a motor phase current reconstruction method. Background Art

[0002] Permanent magnet synchronous motors are usually driven by space vector control, especially in the fields of compressors, blowers, water pumps, electric bicycles, etc. of air conditioning systems, because it is impossible to install position sensors or for cost optimization, it is usually necessary to collect motor phase current to estimate the rotor position of the motor and then drive the motor correctly. The three-resistor current sampling method of the lower bridge of the inverter is widely used because of its low cost and simple control method.

[0003] When using the traditional three-phase current reconstruction algorithm, the lower bridge is turned on for too short a time at high modulation rates, so effective three-phase current cannot be sampled, resulting in the motor not being able to operate normally. At this time, the modulation rate is usually limited to ensure reliable operation of the motor, but this will limit the bus voltage utilization, thus affecting the motor's operating efficiency. Summary of the invention

[0004] In view of the above-mentioned technical deficiencies, the technical problem to be solved by the present invention is to provide a motor phase current reconstruction method, aiming to solve the problem that the lower bridge opening time is too short at high modulation rate, and the influence of switching noise, and the three-phase current cannot be effectively sampled.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solution: The present invention provides a motor phase current reconstruction method, comprising:

[0006] S1, obtain the PWM trigger counter value of the driving tube switch signal of the next cycle, and determine the ADC current sampling point of the next cycle according to the sequence of the three lower bridge PWM triggers, the size of the trigger counter value and the minimum sampling window time;

[0007] S2, sampling the current according to the ADC current sampling point of the next cycle, wherein it is determined whether the phase current of the motor can be directly sampled through the resistor of the lower bridge, and if the phase current of the motor cannot be directly sampled, the phase current is reconstructed by Kirchhoff's current law or by low-pass filtering;

[0008] S3. Based on the ADC current sampling points of the next cycle, the delay amount of the estimated motor position is calculated, and the delay amount is added to the motor rotor angle estimated in the next cycle as a time delay component to obtain the compensated motor rotor angle.

[0009] Further, the values ​​of the A, B, and C three-phase PWM trigger counters of the next cycle are compared;

[0010] The size of the A, B, C three-phase PWM trigger counter value of the next cycle obtained by comparison is used to represent the minimum sampling window time that can meet the phase current sampling;

[0011] The ADC current sampling point of the next cycle is obtained based on the minimum sampling window time of the phase current sampling.

[0012] Furthermore, the time of the minimum sampling window is twice the sum of the sampling noise time, the ADC processing time and the driver tube shutdown time.

[0013] Furthermore, the minimum value of the A, B, and C three-phase PWM trigger counter values ​​of the next cycle obtained by comparison is set as CMP min , the middle value is set to CMP med , the maximum value is set to CMP max ;

[0014] Set the ADC current sampling point of the next cycle to T trigger And the minimum sampling window time is T ADCmin ;

[0015] When CMP min >T ADCmin When , it means that the three-phase currents can be collected in the conduction window of the phase PWM; the ADC current sampling point of the next cycle is set to the half time point of the sampling window, that is, T trigger =0.5×CMP min .

[0016] Furthermore, when CMP min <T ADCmin When CMP med -CMP min >T ADCmin , it means that the two-phase currents corresponding to the middle and maximum values ​​of the A, B, C three-phase PWM trigger counter values ​​of the next cycle can be collected in the window where the phase current corresponding to the minimum value of the A, B, C three-phase PWM trigger counter values ​​of the next cycle is turned off and the phase current corresponding to the middle value of the A, B, C three-phase PWM trigger counter values ​​of the next cycle is turned on. At this time, the ADC current sampling point of the next cycle is set to the half time point of the sampling window, that is, T trigger =0.5×(CMP med -CMP min ).

[0017] Furthermore, when CMP min <T ADCmin When CMP med -CMP min <T ADCmin, it means that only the phase current corresponding to the maximum value of the A, B, and C three-phase PWM trigger counter value in the next cycle can be collected in the window where the remaining two phase currents are turned off and the current of the phase is turned on. At this time, the ADC current sampling point of the next cycle is set to the time point of half of the sampling window, that is, T trigger =0.5×(CMP max -CMP med ).

[0018] Furthermore, if the current value of one phase cannot be collected directly, Kirchhoff's current law is used to calculate the missing current value of one phase through the current values ​​of the remaining two phases, or the three-phase motor current reconstruction value of the previous cycle is obtained. The three-phase motor current reconstruction value of the previous cycle is passed through a low-pass filter as the sampling current value of the next cycle.

[0019] Furthermore, if there are two-phase current values ​​that cannot be directly collected, the reconstructed value of the three-phase motor current of the previous cycle is passed through a low-pass filter as the sampled current value of the next cycle.

[0020] Further, according to the calculated ADC current sampling point T of the next cycle trigger , set each PWM cycle value T period and the motor speed ω estimated by the inverter, the delay amount of the motor estimated position is calculated as follows:

[0021] θ=ω×(T period -T trigger ) / T period

[0022] Where θ is the delay in estimating the motor position.

[0023] Furthermore, the compensation amount is calculated based on the delay amount of the motor estimated position, and the calculated deviation angle caused by the position offset of the ADC current sampling point is corrected as follows:

[0024] W=0.5×ω×T pwm ×θ=0.5×ω×T pwm ×(T period -T trigger ) / T period

[0025] The compensated electronic rotor angle is as follows:

[0026] θ(k+1)=θ_cal+W=θ_cal+0.5×ω×T pwm ×(T period -T trigger ) / T period

[0027] Where W is the compensation amount, θ_cal is the motor rotor angle estimated by the position estimator in the current cycle, θ(k+1) is the motor rotor angle after compensation, and T pwm is the pulse width of one PWM cycle.

[0028] The beneficial effects of the present invention are:

[0029] 1. The present invention improves the accuracy and stability of the current signal by translating the sampling point and avoiding switching noise, combined with low-pass filtering.

[0030] 2. The present invention improves the accuracy of motor rotor angle estimation by calculating and compensating for the angle delay caused by sampling point offset, thereby achieving stable control at high speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 This is a general schematic diagram of three-resistance sampling for frequency converters.

[0033] Figure 2 This is a diagram of ADC current sampling point settings for a motor phase current reconstruction method according to the present invention.

[0034] Figure 3 Schematic diagram of the minimum sampling window of phase current of the present invention.

[0035] Figure 4 This is the angle compensation correction diagram of the traditional current-free reconstruction method.

[0036] Figure 5 This is the angle compensation correction diagram of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] like Figure 1As shown, a variable frequency drive without a position sensor generally adopts a three-phase full-bridge topology, including the upper-bridge drive transistors of AH, BH, and CH, and the lower-bridge drive transistors of AL, BL, and CL. In addition, three lower-bridge resistors, namely R1shunt, R2shunt, and R3shunt, are used for sampling, and the rotor position of the motor is calculated through a position estimator for space vector control.

[0040] As Figure 2 shown, this embodiment provides a method for reconstructing the motor phase current, including:

[0041] Obtain the PWM trigger counter values of the drive transistor switching signals for the next cycle. According to the sequence of the three lower-bridge PWM triggers and the magnitudes of the trigger counter values, calculate the first, second, and third time points of the falling edges of the three PWMs; further calculate the minimum sampling window time that can satisfy the phase current sampling, thereby determining the ADC current sampling point for the next cycle.

[0042] As Figure 3 shown, the time of the minimum sampling window is 2 times the sum of the sampling noise time, the ADC processing time, and the drive transistor turn-off time, that is, T ADCmin = 2×(T noise + T ADC_sample + T d_off ).

[0043] Compare the magnitudes of the PWM trigger counter values of phases A, B, and C for the next cycle; use the magnitudes of the PWM trigger counter values of phases A, B, and C for the next cycle obtained from the comparison to represent the minimum sampling window time that can satisfy the phase current sampling; obtain the ADC current sampling point for the next cycle based on the minimum sampling window time of the phase current sampling.

[0044] In this embodiment, CMPA, CMPB, and CMPC are the PWM trigger counter values of phases A, B, and C for the current cycle. Set the ADC current sampling point for the next cycle as T trigger and the time of the minimum sampling window as T ADCmin ;

[0045] Assume CMPA < CMPB < CMPC, then:

[0046] When CMPA > T ADCmin , it means that all three-phase currents can be sampled within the conduction window of the A-phase PWM; the ADC current sampling point for the next cycle is set as half of the sampling window time point, that is, T trigger = 0.5×CMP min ; At this time, the three-phase currents of A, B, and C can all be sampled through the resistors of the lower bridge. The motor phase current of the current cycle is the actual sampled current:

[0047] Ia(k)=Ia_sample

[0048] Ib(k)=Ib_sample

[0049] Ic(k)=Ic_sample

[0050] When CMPA <T ADCmin When CMPB-CMPA>T ADCmin , which means that the currents of phases B and C can be collected in the window when the current of phase A is turned off and the current of phase B is turned on. At this time, the ADC current sampling point of the next cycle is set to the time point of half of the sampling window, that is, T trigger =0.5×(CMP med -CMP min ); At this time, the A phase current uses the current value of the actual filter feedback, and the B and C phase currents use the actual sampling current, that is,

[0051] Ia(k)=Ia(k-1)+0.5*(Ia_sample(k)–Ia(k-1))

[0052] Or Ia(k)=-(Ib_sample(k)+Ic_sample(k))

[0053] Ib(k)=Ib_sample

[0054] Ic(k)=Ic_sample

[0055] When CMPA <T ADCmin When CMPB-CMPA <T ADCmin , it means that only the C phase current can be collected in the window when the A and B phase currents are turned off and the C phase current is turned on. At this time, the ADC current sampling point of the next cycle is set to the time point of half of the sampling window, that is, T trigger =0.5×(CMP max -CMP med ); At this time, the A and B phase motor currents use the current values ​​of actual filter feedback, and the C phase current uses the actual sampling current:

[0056] Ia(k)=Ia(k-1)+0.5×(Ia_sample(k)–Ia(k-1))

[0057] Ib(k)=Ib(k-1)+0.5×(Ib_sample(k)–Ib(k-1))

[0058] Ic(k)=Ic_sample

[0059] Among them, Ia(k), Ib(k) and Ic(k) are the reconstructed current values ​​of phase A, B and C of the current cycle respectively, Ia(k-1), Ib(k-1) and Ic(k-1) are the reconstructed current values ​​of phase A, B and C of the previous cycle respectively, and Ia_sample(k), Ib_sample(k) and Ic_sample(k) are the sampled current values ​​of phase A, B and C of the current cycle respectively.

[0060] According to the calculated ADC current sampling point T of the next cycle trigger , set each PWM cycle value T period and the motor speed ω estimated by the inverter, the delay amount of the motor estimated position is calculated as follows:

[0061] θ=ω×(T period -T trigger ) / T period

[0062] Where θ is the delay in estimating the motor position.

[0063] The compensation amount is calculated based on the delay amount of the motor estimated position, and the calculated deviation angle caused by the position offset of the ADC current sampling point is corrected as follows:

[0064] W=0.5×ω×T pwm ×θ=0.5×ω×T pwm ×(T period -T trigger ) / T period

[0065] The compensated electronic rotor angle is as follows:

[0066] θ(k+1)=θ_cal+W=θ_cal+0.5×ω×T pwm ×(T period -T trigger ) / T period

[0067] Where W is the compensation amount, θ_cal is the motor rotor angle estimated by the position estimator in the current cycle, θ(k+1) is the motor rotor angle after compensation, and T pwm is the pulse width of one PWM cycle.

[0068] Example 2

[0069] This embodiment is the second embodiment of the present invention. This embodiment is different from the first embodiment in that it provides a verification test of a motor phase current reconstruction method to verify and illustrate the technical effects adopted in this method.

[0070] like Figure 4As shown, the inverter estimates the motor speed ω, and each current sampling results in the PWM counter counting in UP-Down mode, and the counting cycle value is set to T Period , since the angle estimated in the current cycle will be used in the space vector control of the next cycle.

[0071] In the traditional current-free reconstruction method, the current sampling point of each cycle is fixed at the moment when the counter is 0. At this moment, the angle deviation is generally calculated based on 0.5 PWM cycle (T period ),Right now

[0072] θ1(k+1)=θ1_cal+0.5×ω×T pwm

[0073] Among them, θ1(k+1) is the motor rotor angle used for FOC control such as Clark and Park transformation in the next cycle, θ1_cal is the motor rotor angle estimated by the position estimator in the current cycle, T pwm is the pulse width of one PWM cycle.

[0074] like Figure 5 As shown, using the method of the present invention, due to the position offset of the ADC current sampling point, the calculated deviation angle needs to be further corrected:

[0075] W=0.5×ω×T pwm ×(T period -T trigger ) / T period

[0076] The rotor angle after further compensation is as follows:

[0077] θ(k+1)=θ_cal+0.5×ω×T pwm ×(T period -T trigger ) / T period

[0078] Preferably, according to this embodiment, with a permanent magnet synchronous motor with P=4 pole pairs, running at n=11000rpm, an MCU with a main frequency of 100MHz, a motor FOC control main interrupt frequency of 20KHz, and PWM generation in up-down mode, the following is calculated:

[0079] T pwm =50us

[0080] T period =2500

[0081] ω 11000 =2×PI×P×ω 11000 / 60=4605(rad / s)

[0082] Run at a high speed of 11000 rpm, θ(k+1)=θ_cal+0.115×(2500-T trigger ) / 2500; minimum compensation, T trigger Approximately 0, the compensation angle is 0.115rad, that is, 13.18°; in the case of maximum compensation, the Trigger is approximately 1250, and the compensation angle is 0.0575rad, that is, 6.59°; it can be seen that through a reasonable compensation angle, the operating efficiency of the inverter can be optimized, precise position control can be achieved, and excellent motor load capacity can be achieved.

[0083] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A motor phase current reconstruction method, characterized in that: include: S1, obtain the PWM trigger counter value of the driving tube switch signal of the next cycle, and determine the ADC current sampling point of the next cycle according to the sequence of the three lower bridge PWM triggers, the size of the trigger counter value and the minimum sampling window time; S2, sampling the current according to the ADC current sampling point of the next cycle, wherein it is determined whether the phase current of the motor can be directly sampled through the resistor of the lower bridge, and if the phase current of the motor cannot be directly sampled, the phase current is reconstructed by Kirchhoff's current law or by low-pass filtering; S3. Based on the ADC current sampling points of the next cycle, the delay amount of the estimated motor position is calculated, and the delay amount is added to the motor rotor angle estimated in the next cycle as a time delay component to obtain the compensated motor rotor angle.

2. A motor phase current reconstruction method as claimed in claim 1, characterized in that: Compare the values ​​of the A, B, and C three-phase PWM trigger counters in the next cycle; The size of the A, B, C three-phase PWM trigger counter value of the next cycle obtained by comparison is used to represent the minimum sampling window time that can meet the phase current sampling; The ADC current sampling point of the next cycle is obtained based on the minimum sampling window time of the phase current sampling.

3. A motor phase current reconstruction method as claimed in claim 1, characterized in that: The minimum sampling window time is twice the sum of the sampling noise time, the ADC processing time and the driver tube shutdown time.

4. A motor phase current reconstruction method as claimed in claim 2, characterized in that: The minimum value of the A, B, and C three-phase PWM trigger counter values ​​of the next cycle obtained by comparison is set as CMP min , the middle value is set to CMP med , the maximum value is set to CMP max ; Set the ADC current sampling point of the next cycle to T trigger And the minimum sampling window time is T ADCmin ; When CMP min >T ADCmin When , it means that the three-phase currents can be collected in the conduction window of the phase PWM; the ADC current sampling point of the next cycle is set to the half time point of the sampling window, that is, T trigger =0.5×CMP min .

5. A motor phase current reconstruction method as claimed in claim 4, characterized in that: When CMP min <T ADCmin When CMP med -CMP min >T ADCmin , it means that the two-phase currents corresponding to the middle and maximum values ​​of the A, B, C three-phase PWM trigger counter values ​​of the next cycle can be collected in the window where the phase current corresponding to the minimum value of the A, B, C three-phase PWM trigger counter values ​​of the next cycle is turned off and the phase current corresponding to the middle value of the A, B, C three-phase PWM trigger counter values ​​of the next cycle is turned on. At this time, the ADC current sampling point of the next cycle is set to the half time point of the sampling window, that is, T trigger =0.5×(CMP med -CMP min ).

6. A motor phase current reconstruction method as claimed in claim 5, characterized in that: When CMP min <T ADCmin When CMP med -CMP min <T ADCmin , it means that only the phase current corresponding to the maximum value of the A, B, and C three-phase PWM trigger counter value in the next cycle can be collected in the window where the remaining two phase currents are turned off and the current of the phase is turned on. At this time, the ADC current sampling point of the next cycle is set to the time point of half of the sampling window, that is, T trigger =0.5×(CMP max -CMP med ).

7. A motor phase current reconstruction method as claimed in claim 1, characterized in that: If the current value of one phase cannot be collected directly, Kirchhoff's current law is used to calculate the missing current value of one phase through the current values ​​of the remaining two phases, or the three-phase motor current reconstruction value of the previous cycle is obtained. The three-phase motor current reconstruction value of the previous cycle is passed through a low-pass filter as the sampling current value of the next cycle.

8. A motor phase current reconstruction method as claimed in claim 7, characterized in that: If there are two-phase current values ​​that cannot be directly collected, the reconstructed value of the three-phase motor current of the previous cycle is passed through a low-pass filter as the sampled current value of the next cycle.

9. A motor phase current reconstruction method as claimed in claim 1, characterized in that: According to the calculated ADC current sampling point T of the next cycle trigger , set each PWM cycle value T period and the motor speed ω estimated by the inverter, the delay amount of the motor estimated position is calculated as follows: θ=ω×(T period -T trigger ) / T period Where θ is the delay in estimating the motor position.

10. A motor phase current reconstruction method as claimed in claim 9, characterized in that: The compensation amount is calculated based on the delay amount of the motor estimated position, and the calculated deviation angle caused by the position offset of the ADC current sampling point is corrected as follows: W=0.5×ω×T pwm ×θ=0.5×ω×T pwm ×(T period -T trigger ) / T period The compensated electronic rotor angle is as follows: θ(k+1)=θ_cal+W=θ_cal+0.5×ω×T pwm ×(T period -T trigger ) / T period Where W is the compensation amount, θ_cal is the motor rotor angle estimated by the position estimator in the current cycle, θ(k+1) is the motor rotor angle after compensation, and T pwm is the pulse width of one PWM cycle.

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