A single bus current sampling and less phase-shifting phase current reconstruction method

Abstract

A single bus current sampling few-phase-shifted phase current reconstruction method, based on an extended electromotive force (EEMF) model, uses coordinate transformation to design a current observer on the abc axis, estimates the current of the other two phases using the current of any one phase, thereby reducing the phase shift of the wave generation and reducing the electromagnetic noise and power loss generated thereby; the invention divides the calculation duty cycle into five states after center alignment, determines which phase of U, V and W the effective current value obtained by sampling corresponds to according to flags V Sector and S shift , if only one effective current value can be obtained, a corresponding current observer is designed, and the invention uses a sliding mode observer to reconstruct three-phase current; the reconstructed three-phase current can be distributed to the U, V and W three-phase drive control circuits of the motor according to the sector situation, achieving the effect of motor control.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of motor control and relates to a phase current reconstruction method with single bus current sampling and less phase shifting. BACKGROUND

[0002] With the development of power electronics technology, permanent magnet synchronous motors are widely used in various product fields such as household appliances, fans, and water pumps due to their wide speed range, high power density, and high reliability. However, whether the permanent magnet synchronous motor and its control system can achieve low cost, low noise, and low loss is a bottleneck restricting its widespread application in the industrial field. Since motor vector control relies on phase current information, the accuracy of stator phase current detection directly affects the overall system performance in actual motor vector control. Therefore, research on phase current reconstruction technology is inevitable. Current sampling schemes currently mainly include phase line isolation current sampling, bridge arm current sampling method, and single bus current sampling method. In small power and low cost drivers, the method of installing a sampling resistor on the bus to collect bus current is commonly used. The sampling resistor is connected to the common end of the lower tube of the three-phase inverter and the ground. When the three-phase pulse width modulation waveform (PWM) is in different states, the bus current can reflect the current of different phases. This method is simply called single resistor sampling.

[0003] For the single resistor sampling problem, the patent "PWM signal generation method suitable for single resistor sampling in motor vector control" (CN 118842393 A, October 25, 2024) proposes a method of determining whether to compensate for the high-level conduction time of PWM in the corresponding sector, and distributing PWM signals to the drive control circuits of the U, V, and W phases of the motor according to the corresponding relationship. However, this method will bring about a large current change because it modifies the PWM, and the noise caused by single resistor sampling control is more obvious. Furthermore, the literature "Optimal current reconstruction strategy utilizing various PWM switching generation schemes in DC-link single shunt resistor" (Byun M H, Park M S. Journal of Power Electronics, 2024) proposes an optimal current reconstruction strategy suitable for all non-measurable regions, which divides the non-measurable region into three parts and selectively applies various pulse width modulation techniques, requiring only simple calculations to achieve control effects. However, compared with the previous method, the electromagnetic noise of the motor during rotation is still obvious. SUMMARY

[0004] In order to solve the problem that single-resistance sampling needs to change PWM wave time in implementation, causes the asymmetric PWM wave, thus generates electromagnetic noise, large current ripple, loss increase and other problems, the application provides a single bus current sampling less phase-shifting phase current reconstruction method. Based on the extended electromotive force (EEMF) model, the current observer on the abc axis is designed by using coordinate transformation, and the currents of the other two phases are estimated by using any one phase current, so that the phase-shifting of wave emission is reduced, and the electromagnetic noise and power loss generated thereby are reduced.

[0005] In order to achieve the above object, the technical scheme adopted by the application is:

[0006] A single bus current sampling less phase-shifting phase current reconstruction method, comprising the following steps:

[0007] Step S1, determining the minimum sampling window time T min and the sampling delay time T Delay according to the experimental platform.

[0008] Step S2, based on seven-segment space vector pulse-width modulation (SVPWM), the duty cycles corresponding to U, V and W three phases in different sectors are calculated, and the sector flag V Sector is assigned.

[0009] Step S3, according to the calculated duty cycles, the duty cycles are placed in the middle and aligned, and the rising trigger threshold point and the falling trigger threshold point of three-phase PWM in single rising count mode are calculated.

[0010] Step S4, according to the rising trigger threshold point and the falling trigger threshold point of three-phase PWM, the rising trigger threshold point difference T Delta1 of the intermediate duty cycle phase and the maximum duty cycle phase in different sectors, and the rising trigger threshold point difference T Delta2 of the minimum duty cycle phase and the intermediate duty cycle phase are calculated.

[0011] Step S5, the calculated rising trigger threshold point differences T Delta1 and T Delta2 are compared with the minimum sampling window time T min respectively, and the flag S shift is assigned.

[0012] Step S6, according to the values of the flags V Sector and S shift , the rising trigger threshold point and the falling trigger threshold point of the final three-phase PWM in single rising count mode, and the corresponding sampling time threshold points T samp1 and Tsamp2 ;

[0013] Step S7: Based on flag V Sector and S shift The sampling determines which phase (U, V, W) current value is obtained, and the three-phase current is reconstructed using the corresponding current observer.

[0014] Furthermore, in step S5, T is calculated respectively. min With T Delta1 and T Delta2 The difference between D1 and D2 is used to obtain D1 and D2. Based on the values ​​of D1 and D2, five states can be obtained, and the flag S is assigned a value. shift :

[0015] State 1: No phase shift is required in normal state, S shift =1;

[0016] State 2: Using T samp2 The sampled current value does not require phase shifting, S shift =2;

[0017] State 3: Using T samp1 The sampled current value does not require phase shifting, S shift =3;

[0018] State 4: Using T samp1 The sampled current value needs to be phase-shifted, S shift =4;

[0019] Status 5: Using T samp2 The sampled current value needs to be phase-shifted, S shift =5.

[0020] Furthermore, in step S6, based on the flag bit V Sector and S shift The values ​​are discussed in categories. When no phase shift is needed, the trigger threshold point remains unchanged. If phase shift is required, corresponding changes are made to determine the final rising and falling trigger threshold points of the three-phase PWM in single rising counting mode. The calculation formula for phase a is as follows (it can also be phase b or phase c):

[0021]

[0022]

[0023] Among them, T a_upold T a_downold In step S3, based on the calculated duty cycle, the duty cycle is centered and aligned, and the calculated rising and falling trigger threshold points of the three-phase PWM in single rising counting mode are obtained; T a_up Ta_down The updated final rising trigger threshold point and falling trigger threshold point; D is the corresponding phase shift distance, and the calculation formula of D is as follows:

[0024]

[0025] Further, in the step S7, according to the flag V Sector and S shift , it is determined which phase of U, V, W the sampled current value is, and the calculation process of reconstructing the three-phase current through the corresponding current observer is as follows:

[0026] According to the EEMF mathematical model, the stator motion equation of the motor can be obtained as:

[0027]

[0028] Taking phase a as an example (or phase b or phase c), assuming that the a-phase current can be sampled, the a-phase current needs to be used alone to ensure the stable operation of the motor, and according to the inverse Clarke transformation, the current is transformed from the static coordinate system αβ axis system to the natural coordinate system abc axis system, and the transformation formula is as follows:

[0029] Substitute equation (5) into equation (4), and transform i α , i β in equation (4) into i a , i b , and the transformed equation is:

[0030]

[0031] wherein,

[0032] According to equation (6), an a-phase sliding mode current observer taking the abc-axis current as a state variable is constructed:

[0033]

[0034] wherein, is a saturation function, and the saturation function is defined as follows:

[0035]

[0036] wherein, x is a, b, c, and ξ is a set comparison value;

[0037] In the a-phase current observer, when the state variable converges to the actual a-phase current i aWhen the b-axis current estimation value converges to the actual value, the a-axis current estimation value will also converge to the actual value; similarly, if only the b-phase current can be sampled, a current observer needs to be constructed from the detected b-phase current value for control;

[0038] If only the c-phase current can be sampled, a current observer needs to be constructed from the detected c-phase current value for control, because the vector sum of the three-phase currents is equal to zero, so i b can be expressed as i a and i c , that is,

[0039] i b = -i a -i c (9)

[0040] Substituting equation (9) into equation (5) and substituting equation (4) after rearrangement and transformation, the c-phase current observer is obtained, when the state variable converges to the actual c-phase current i c , the a-axis current estimation value will also converge to the actual value, the value of the current i b is calculated according to equation (9), and the three-phase current is reconstructed.

[0041] So far, a single bus current sampling and phase-shifting few phase current reconstruction method of the application has been completed. The application divides the calculation duty cycle into five states after center alignment, and determines which phase of U, V and W the effective current value obtained by sampling corresponds to according to the flag bits V Sector and S shift . If only one effective current value can be obtained, a corresponding current observer is designed, and the application uses a sliding mode observer to reconstruct the three-phase current. As for using the same idea to design other types of current observers, it is also within the protection scope of the application. The reconstructed three-phase current can be distributed to the U, V and W three-phase drive control circuits of the motor according to the sector situation, to achieve the effect of motor control.

[0042] Compared with the prior art, the application has the following beneficial effects:

[0043] 1) When the motor runs to the unobservable area, the PWM phase-shifting can be reduced or even eliminated, the current ripple caused by phase-shifting is reduced, and the problems such as high loss and noise caused by phase-shifting are weakened;

[0044] 2) By transforming the motor mathematical model to the abc axis, only one-phase current information is used to estimate the other two-phase currents, accurate three-phase phase current reconstruction and magnetic field oriented vector control are realized. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The algorithm flowchart of the application;

[0046] Figure 2 The five state diagrams in step S5 of the algorithm of the application;

[0047] Figure 3 The control block diagram of the application;

[0048] Figure 4 The overall diagram of the algorithm simulation verification of the application;

[0049] Figure 5 The acceleration detail diagram at 0.2s of the algorithm simulation verification of the application;

[0050] Figure 6 The load detail diagram at 0.4s of the algorithm simulation verification of the application;

[0051] Figure 7 The deceleration detail diagram at 0.6s of the algorithm simulation verification of the application;

[0052] Figure 8 The load reduction detail diagram at 0.8s of the algorithm simulation verification of the application. DETAILED DESCRIPTION

[0053] The application will be further described below with reference to the accompanying drawings.

[0054] Reference Figures 1-8 A single bus current sampling few-phase phase current reconstruction method, by dividing the duty cycle calculated by the conventional seven-segment SVPWM algorithm into five states, according to the flag V Sector and S shift , determine which item in UVW the effective current sampled corresponds to. By processing the stator voltage equation of the motor, a three-phase current observer is designed to estimate the other two-phase current with one-phase current. The corresponding current observer is used to reconstruct the three-phase current, which is distributed to the three-phase drive control circuit of the motor according to the sector condition, to achieve the effect of motor control.

[0055] The method, as shown in Figure 1 , comprises the following steps:

[0056] Step S1, according to the experimental platform, determine the minimum sampling window time T min and the sampling delay time T Delay ;

[0057] Step S2, based on the seven-segment SVPWM algorithm, calculate the duty cycle corresponding to each of U, V, and W three-phase in different sectors, and assign the sector flag V Sector ;

[0058] Step S3, calculate the rising trigger threshold point and the falling trigger threshold point of the three-phase PWM in the single rising count mode, with the duty cycle centered and aligned;

[0059] Step S4, according to the rising trigger threshold point and the falling trigger threshold point of the three-phase PWM, the rising trigger threshold point difference T Delta1 between the intermediate duty ratio phase and the maximum duty ratio phase in different sectors is calculated Delta2 ;

[0060] Step S5, as Figure 2 shown, the calculated rising trigger threshold point difference T Delta1 and T Delta2 are compared with the minimum sampling window time T min respectively, and the flag bit S shift is assigned, the process is as follows:

[0061] Step 5.1: the difference between T min , T Delta1 and T Delta2 is calculated to obtain D1, D2 respectively:

[0062]

[0063] Step 5.2: according to the values of D1 and D2, five states are divided (state flag bit: S shift ), among which:

[0064] State 1: T Delta1 and T Delta2 are greater than or equal to T min (D1≤0&D2≤0), normal state does not need to be phase shifted, S shift =1;

[0065] State 2: T Delta1 is less than T min (D1>0), T Delta2 is greater than or equal to T min (D2≤0), the current value obtained by T samp2 sampling is used, and no phase shift is needed, S shift =2;

[0066] State 3: T Delta1 is greater than or equal to T min (D1≤0), T Delta2 is less than T min (D2>0), the current value obtained by T samp1 sampling is used, and no phase shift is needed, S shift =3;

[0067] State 4: T Delta1 and T Delta2 are both less than T min and T Delta1 ≥TDelta2 (0 < D1 ≤ D2), using T samp1 the sampled current value needs to be phase-shifted, S shift = 4;

[0068] State 5: T Delta1 and T Delta2 are both less than T min and T Delta1 < T Delta2 (0 < D2 < D1), using T samp2 the sampled current value needs to be phase-shifted, S shift = 5;

[0069] Step S6, according to the values of flags V Sector and S shift , determine the rising trigger threshold point and the falling trigger threshold point of the final three-phase PWM in the single rising count mode, and the corresponding sampling time threshold point T samp1 and T samp2 ; the process is as follows:

[0070] Step 6.1: according to the values of flags V Sector and S shift , update the rising and falling trigger threshold point values of each phase, and the calculation formula is as follows:

[0071]

[0072] wherein, T x_upold , T x_downold (x is a, b, c) are the duty cycles calculated in step S3, the duty cycles are placed in the center of the alignment, and the rising trigger threshold point and the falling trigger threshold point of the three-phase PWM in the single rising count mode are calculated; T x_up , T x_down (x is a, b, c) are the updated final rising trigger threshold point and the falling trigger threshold point; D is the corresponding phase shift distance, and the calculation formula of D is as follows:

[0073]

[0074] Step 6.2: after determining the rising trigger threshold point and the falling trigger threshold point of the final three-phase PWM in the single rising count mode, determine the sampling time threshold point, and the calculation formula is as follows:

[0075]

[0076] Step S7, according to flags V Sector and S shift , determine which phase of U, V, W the sampled current value is, and reconstruct the three-phase current through the corresponding current observer; the process is as follows:

[0077] Step 7.1: According to the flag bit V Sector and S shift , determine the effective sampling current i x_samp case:

[0078]

[0079] Step 7.2: According to the effective sampling current case, reconstruct the three-phase current;

[0080] If two-phase currents can be effectively sampled, since the vector sum of three-phase currents is equal to zero, the third-phase current can be represented by the sampled two-phase currents;

[0081] If only one-phase current can be effectively sampled, a current observer is designed to estimate the other two-phase currents by processing the stator voltage equation of the motor using one-phase current;

[0082] According to the EEMF model, the motor's stator motion equation is obtained as:

[0083]

[0084] Assuming that the a-phase current can be sampled, the a-phase current needs to be used alone to ensure stable operation of the motor. According to the inverse Clarke transformation, the current is transformed from the stationary coordinate system αβ axis system to the natural coordinate system abc axis system, and the transformation formula is as follows:

[0085] Substitute equation (22) into equation (21), and transform i α , i β in equation (21) to i a , i b , and the transformed equation is:

[0086]

[0087] where,

[0088] According to equation (23), an a-phase current observer is constructed with abc-axis currents as state variables:

[0089]

[0090] where, is a saturation function, and the saturation function is defined as follows:

[0091]

[0092] where x is a, b, c, and ξ is a set comparison value.

[0093] In the a-phase current observer, when the state variable converges to the actual a-phase current i a , the b-axis current estimation value will also converge to the actual value; similarly, if only the b-phase current can be sampled, a b-phase current observer shown in equation (26) is needed to be constructed for control:

[0094]

[0095] If only the c-phase current can be sampled, a current observer needs to be constructed using the detected c-phase current value for control, because the vector sum of three-phase currents is equal to zero, so i b is expressed by i a and i c , that is:

[0096] i b = -i a -i c (27)

[0097] Substitute equation (27) into equation (22), and after rearrangement and transformation, we get:

[0098] Substitute equation (28) into equation (21), and after rearrangement and transformation, we get:

[0099]

[0100] wherein,

[0101] According to equation (29), a c-phase current observer with abc-axis current as the state variable is constructed:

[0102]

[0103] In the c-phase current observer, when the state variable converges to the actual c-phase current i c , the a-axis current estimation value will also converge to the actual value, the value of current i b is calculated according to equation (27), and the three-phase current is reconstructed.

[0104] So far, a single bus current sampling and phase-shifting few phase current reconstruction method of the application has been completed. The application divides the corresponding duty cycles of U, V and W three-phase under different sectors calculated based on the conventional seven-segment SVPWM algorithm into five states after center alignment, wherein the normal sampling calculation running section corresponds to state 1, the current value sampled by T samp2 is directly used for operation reconstruction section corresponding to state 2, and the current value sampled by T samp1The current value sampled is calculated to reconstruct the corresponding state 3, and T is used after phase shift samp1 The current value sampled is calculated to reconstruct the corresponding state 4, and T is used after phase shift samp2 The current value sampled is calculated to reconstruct the corresponding state 5. According to the flag V Sector and S shift , determine which phase of U, V, W the current value sampled is, if only one effective current value can be sampled, then through the design of the corresponding current observer, the sliding mode observer is used to reconstruct the three-phase current; as for using the same idea, designing other types of current observers, also within the protection scope of the application. The reconstructed three-phase current can be distributed to the U, V, W three-phase drive control circuit of the motor according to the sector condition, to realize the effect of motor control.

[0105] Finally, the effectiveness of the single bus current sampling and phase shift of the phase current reconstruction method of the application is illustrated through simulation. Figure 4

[0106] In MATLAB, the given system parameters are simulated, and Table 1 is a system parameter table.

[0107]

[0108]

[0109] Table 1

[0110] Figure 4 The three-phase actual current and estimated current comparison simulation diagram obtained by simulating 1s is shown, wherein the blue line is the actual current value of each phase, and the red line is the corresponding estimated current value of each phase. The initial speed given in the simulation is 0.3 (pu, same below), and the initial load given is 0.5 (pu, same below). At 0.2s, the speed given is accelerated from 0.3 to 0.6, and the local detail diagram obtained is shown in Figure 5 At 0.4s, the load given is loaded from 0.5 to 0.8, and the local detail diagram obtained is shown in Figure 6 At 0.6s, the speed given is decelerated from 0.6 to 0.3, and the local detail diagram obtained is shown in Figure 7 Finally, at 0.8s, the load given is unloaded from 0.8 to 0.5, and the local detail diagram obtained is shown in Figure 8 Finally, at 0.8s, the load given is unloaded from 0.8 to 0.5, and the local detail diagram obtained is shown in

[0111] ​In summary, through simulation operation, it can be seen that under the control of the single bus current sampling and small phase-shifting phase current reconstruction method, the current observer can follow the change of the actual current under different given conditions (acceleration, deceleration, loading, and unloading), and the algorithm can realize the effect of servo motor control.

[0112] The above-described embodiments are only used to illustrate the relatively specific and detailed embodiments described in the application, but cannot be understood as limiting the scope of the application. It should be noted that for those skilled in the art, it is obvious that several modifications and improvements can be made. The technical solutions of the application are modified or replaced equivalently without departing from the purpose and scope of the technical solutions of the application, which should be covered in the scope of the claims of the application. Therefore, the protection scope of the application should be subject to the appended claims.

Claims

1. A phase current reconstruction method with minimal phase shift during single bus current sampling, characterized in that, The method includes the following steps: Step S1: Determine the minimum sampling window time T based on the experimental platform. min and sampling delay time T Delay ; Step S2: Based on seven-segment space vector pulse width modulation (SVPWM), calculate the duty cycle of each of the three phases U, V, and W under different sectors, and assign the sector flag bit V to it. Sector ; Step S3: Based on the calculated duty cycle, center and align the duty cycle, and calculate the rising trigger threshold and falling trigger threshold of the three-phase PWM in single rising counting mode. Step S4: Based on the rising and falling trigger threshold points of the three-phase PWM, calculate the difference T between the rising trigger threshold points of the middle duty cycle phase and the maximum duty cycle phase in different sectors. Delta1 And the difference T between the rising trigger threshold points of the minimum duty cycle phase and the intermediate duty cycle phase. Delta2 ; Step S5: Calculate the difference T between the rising trigger threshold points. Delta1 and T Delta2 Compared with the minimum sampling window time T respectively min Compare and assign values ​​to flag S. shift The process is as follows: Step 5.1: Calculate T separately min With T Delta1 and T Delta2 The difference between D1 and D2 is: Step 5.2: Divide the data into five states based on the values ​​of D1 and D2, where: State 1: T Delta1 and T Delta2 All are greater than or equal to T min Under normal conditions, phase shifting is not required. shift =1; State 2: T Delta1 Less than T min T Delta2 Greater than or equal to T min Using T samp2 The sampled current value does not require phase shifting, S shift =2; State 3: T Delta1 Greater than or equal to T min T Delta2 Less than T min Using T samp1 The sampled current value does not require phase shifting, S shift =3; State 4: T Delta1 and T Delta2 All less than T min And T Delta1 ≥T Delta2 Using T samp1 The sampled current value needs to be phase-shifted, S shift =4; State 5: T Delta1 and T Delta2 All less than T min And T Delta1 <T Delta2 Using T samp2 The sampled current value needs to be phase-shifted, S shift =5; Step S6: Based on flag V Sector and S shift The values ​​of these values ​​determine the final three-phase PWM rise trigger threshold and fall trigger threshold in single rise counting mode, as well as the corresponding sampling time threshold T. samp1 and T samp2 The process is as follows: Step 6.1: Based on flag V Sector and S shift The value of is used to update the threshold values ​​for each phase's rise and fall, calculated using the following formula: Among them, T x_upold T x_downold In step S3, based on the calculated duty cycles (x = a, b, c), the duty cycles are centered and aligned. The calculated rising and falling trigger thresholds for the three-phase PWM in single-rising counting mode are then used. x_up T x_down Here are the updated final rise trigger threshold and fall trigger threshold; D is the corresponding phase shift distance, calculated using the following formula: Step 6.2: After determining the rising trigger threshold and falling trigger threshold of the final three-phase PWM in single rising counting mode, determine the sampling time threshold. The calculation formula is as follows: Step S7: Based on flag V Sector and S shift To determine which phase (U, V, W) current value was obtained from the sampling, the three-phase current is reconstructed using the corresponding current observer. The process is as follows: Step 7.1: Based on flag V Sector and S shift Determine the effective sampling current i x_samp Situation: Step 7.2: Reconstruct the three-phase current based on the effective sampled current.

2. The phase current reconstruction method with minimal phase shift in single bus current sampling according to claim 1, characterized in that, In step S7, according to the flag bit V Sector and S shift The process of determining which phase (U, V, W) current value was obtained from the sampling and reconstructing the three-phase current using the corresponding current observer is as follows: The stator motion equation of the motor is obtained from the EEMF mathematical model as follows: Taking phase a as an example, assuming that the phase a current is available and needs to be used separately to ensure the stable operation of the motor, according to the inverse Clarke transformation, the current can be transformed from the stationary coordinate system αβ axis to the natural coordinate system abc axis. The transformation formula is as follows: Substituting equation (13) into equation (12), and changing the i in equation (12) α i β Transform into i a i b After transformation, we get the following equation: in, Construct an a-phase sliding mode current observer with abc axis currents as state variables based on equation (14): in, For saturation functions, saturation functions The definition is as follows: Where x represents a, b, and c, and ξ is a set comparison value; In the phase a current observer, when the state variable Converging to the actual current i of phase a a When the phase b current is measured, the estimated value of phase b current will also converge to the actual value. Similarly, if only phase b current can be sampled, a current observer needs to be constructed from the detected phase b current value for control. If only the c-phase current can be sampled, a current observer needs to be constructed using the detected c-phase current value for control, because the vector sum of the three-phase currents is equal to zero, therefore i b You can use i a and i c To represent, that is i b =-i a -i c (17) Substituting equation (17) into equation (13), and then into equation (12), after simplification and transformation, we obtain the c-phase current observer. When the state variable Converging to the actual current i in phase c c At that time, the estimated value of the a-axis current will also converge to the actual value, and the current i can be calculated according to equation (17). b The value of is used to reconstruct the three-phase current.

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