Single-bus current sampling less-phase-shift phase current reconstruction method

Abstract

The invention relates to a single-bus current sampling less-phase-shift phase current reconstruction method, which is based on an extended counter electromotive force (EEMF) model, utilizes coordinate transformation to design a current observer on an abc axis, and uses any phase current to estimate other two phase currents, thereby reducing wave phase shift, and reducing electromagnetic noise and power loss generated by the wave phase shift. According to the method, the calculated duty ratio is divided into five states after being centered and aligned, the phase of U, V and W corresponding to an effective current value obtained through sampling is determined according to flag bits VSector and Sshift, and if only one effective current value can be acquired, a corresponding current observer is designed, and three-phase current is reconstructed by adopting a sliding mode observer; and the reconstructed three-phase current can be distributed to U, V and W three-phase driving control circuits of the motor according to the condition of the sector, so that the effect of motor control is realized.

Description

Technical Field

[0001] The invention 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 Art

[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 regulation range, high power density, and high reliability. Whether permanent magnet synchronous motors and their control systems can achieve low cost, low noise, and low loss is a bottleneck that restricts their widespread application in the industrial field. Since the vector control of the motor depends on the phase current information, in the actual motor vector control process, the accuracy of the stator phase current detection directly affects the overall system performance. Therefore, the research on phase current reconstruction technology is an inevitable choice. The current current sampling schemes mainly include phase line isolation current sampling, bridge arm current sampling method, and single bus current sampling method. In low-power and low-cost drives, the bus current is collected by installing a sampling resistor on the bus. 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 referred to as single resistor sampling.

[0003] In response to the single resistor sampling problem, the patent "PWM signal generation method suitable for single resistor sampling in motor vector control" (CN 118842393 A, 2024.10.25) proposes a method of determining whether to compensate for the high-level conduction time of PWM in the corresponding sector, and distributing the PWM signal to the U, V, and W three-phase drive control circuit of the motor according to the corresponding relationship. However, because this method changes PWM, it will bring about a large current change, and the noise caused by single resistor sampling control is more obvious. Furthermore, the document "Optimal current reconstruction strategy utilizing various PWM switching generation schemes in DC-link single shunt resistor" (Byun MH, Park M S. Journal of Power Electronics, 2024) proposes an optimal current reconstruction strategy applicable to all unmeasurable areas, dividing the unmeasurable area into three parts, and selectively applying various pulse width modulation techniques, and only simple calculations are required to achieve the control effect. However, compared with the previous method, the electromagnetic noise when the motor rotates is still obvious. Summary of the invention

[0004] In order to solve the problem that the PWM wave generation time needs to be changed in the implementation of single resistor sampling, resulting in asymmetric PWM waves, thus generating electromagnetic noise, large current ripple, increased loss and other problems, the present invention proposes a phase current reconstruction method with less phase shift for single bus current sampling. Based on the extended back electromotive force (EEMF) model, the current observer on the abc axis is designed by using coordinate transformation, and the current of any phase is used to estimate the current of the other two phases, thereby reducing the phase shift of the wave generation and reducing the electromagnetic noise and power loss generated by it.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A phase current reconstruction method with single bus current sampling and less phase shifting includes the following steps:

[0007] Step S1: Determine the minimum sampling window time T according to the experimental platform min and sampling delay time T Delay ;

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

[0009] Step S3, according to the calculated duty cycle, align the duty cycle in the center and calculate the rising trigger threshold point and the falling trigger threshold point of the three-phase PWM in the single rising count mode;

[0010] Step S4: 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 according to the rising trigger threshold point and the falling trigger threshold point of the three-phase PWM. Delta1 , and the rising trigger threshold difference value T between the minimum duty cycle phase and the middle duty cycle phase Delta2 ;

[0011] Step S5: calculate the rising trigger threshold value difference T Delta1 and T Delta2 Respectively with the minimum sampling window time T min Compare and assign flag bit S shift ;

[0012] Step S6: According to the flag bit V Sector and S shift The value of determines the rising trigger threshold point and falling trigger threshold point of the final three-phase PWM in the single rising counting mode, as well as the corresponding sampling time threshold point T samp1 and Tsamp2 ;

[0013] Step S7: According to the flag bit V Sector and S shift , determine which phase of U, V, and W the current value is sampled, and reconstruct the three-phase current through the corresponding current observer.

[0014] Further, in step S5, T min With T Delta1 and T Delta2 The difference is D1 and D2. Five states can be obtained according to the values ​​of D1 and D2. The flag bit S is assigned shift :

[0015] State 1: Normal state does not require phase shifting, S shift =1;

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

[0017] State 3: Using T samp1 The current value obtained by sampling 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] State 5: Using T samp2 The sampled current value needs to be phase shifted, S shift =5.

[0020] Furthermore, in step S6, according to the flag bit V Sector and S shift The value of is discussed by classification. When phase shift is not required, the starting threshold point remains unchanged. If phase shift is required, corresponding changes are made to determine the rising trigger threshold point and falling trigger threshold point of the final three-phase PWM in single rising count 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 The duty cycle calculated in step S3 is aligned in the center, 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 a_up 、Ta_down are 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] Furthermore, in step S7, according to the flag bit V Sector and S shift , determine which phase of U, V, W the current value is sampled from, and reconstruct the calculation process of the three-phase current through the corresponding current observer as follows:

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

[0027]

[0028] Take phase a as an example (it can also be phase b or phase c), assuming that the current of phase a is available, and the current of phase a needs to be used alone to ensure the 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. The transformation formula is as follows:

[0029]

[0030] Substitute equation (5) into equation (4), and replace i in equation (4) α 、i β Transform to i a 、i b , after transformation, we get the equation:

[0031]

[0032] in,

[0033] According to equation (6), the a phase sliding mode current observer with the abc axis current as the state variable is constructed:

[0034]

[0035] in, is a saturation function. The definition is as follows:

[0036]

[0037] Among them, x is a, b, c, and ξ is the set comparison value;

[0038] In the a-phase current observer, when the state variable Converges to the actual current i of phase a aWhen , the estimated value of the b-axis current will also converge to the actual value; similarly, if only the b-phase current can be sampled, it is necessary to construct a current observer based on the detected b-phase current value for control;

[0039] If only the c-phase current can be sampled, the current observer needs to be constructed using the detected c-phase current value for control. Since the vector sum of the three-phase currents is equal to zero, i b You can use a and i c To express, that is

[0040] i b =-i a -i c (9)

[0041] Substitute equation (9) into equation (5), and then into equation (4) to obtain the c-phase current observer after rearrangement and transformation. When the state variable Converges to the actual current i of phase c c When , the estimated value of the a-axis current will also converge to the actual value, and the current i is calculated according to formula (9): b The three-phase current is reconstructed from the value of

[0042] So far, a phase current reconstruction method for single bus current sampling and less phase shifting of the present invention has been completed. The present invention divides the calculated duty cycle into five states after center alignment, according to the flag bit V Sector and S shift , determine which phase of U, V, and W the sampled effective current value corresponds to. If only one effective current value can be sampled, the corresponding current observer is designed. The present invention 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 scope of protection of this patent; 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, thereby achieving the effect of motor control.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1) When the motor runs into the unobservable area, the PWM phase shift can be reduced or even eliminated, thereby reducing the problems of large current ripple and high loss caused by the phase shift, and weakening the noise caused by the phase shift;

[0045] 2) By transforming the mathematical model of the motor into the abc axes, only one-phase current information is used to estimate the other two-phase currents, thereby achieving accurate three-phase current reconstruction and magnetic field-oriented vector control. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the algorithm flow chart of the present invention;

[0047] Figure 2 Schematic diagram of five states in step S5 of the algorithm of the present invention;

[0048] Figure 3 It is a control framework diagram of the present invention;

[0049] Figure 4 It is the general diagram of the algorithm simulation verification of the present invention;

[0050] Figure 5 This is a detailed acceleration diagram at 0.2s for algorithm simulation verification of the present invention;

[0051] Figure 6 The algorithm simulation of the present invention verifies the loading of the detail graph at 0.4s;

[0052] Figure 7 This is a detailed diagram of deceleration at 0.6s for the algorithm simulation verification of the present invention;

[0053] Figure 8 This is a detailed diagram of load reduction at 0.8s for simulation verification of the algorithm of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described below in conjunction with the accompanying drawings.

[0055] Reference Figures 1 to 8 , a phase current reconstruction method with single bus current sampling and less phase shifting, which divides the duty ratio calculated by the conventional seven-segment SVPWM algorithm into five states, according to the flag bit V Sector and S shift , determine which item in UVW the sampled effective current corresponds to. By processing the stator voltage equation of the motor, a three-phase current observer is designed, and one-phase current is used to estimate the other two-phase currents. Using the corresponding current observer, the three-phase current is reconstructed and allocated to the three-phase drive control circuit of the motor according to the sector situation, achieving the effect of motor control.

[0056] The method is as Figure 1 As shown, the following steps are included:

[0057] Step S1: Determine the minimum sampling window time T according to the experimental platform min and sampling delay time T Delay ;

[0058] Step S2: Based on the seven-segment SVPWM algorithm, calculate the corresponding duty ratios of the three phases U, V, and W in different sectors, and assign the sector flag V Sector ;

[0059] Step S3, calculating the rising trigger threshold point and the falling trigger threshold point with the duty cycle aligned in the center under the single rising counting mode of the three-phase PWM;

[0060] Step S4: 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 according to the rising trigger threshold point and the falling trigger threshold point of the three-phase PWM. Delta1 , and the rising trigger threshold difference value T between the minimum duty cycle phase and the middle duty cycle phase Delta2 ;

[0061] Step S5: Figure 2 As shown, the calculated rising trigger threshold spread value T Delta1 and T Delta2 Respectively with the minimum sampling window time T min Compare and assign flag bit S shift , the process is as follows:

[0062] Step 5.1: Calculate T separately min With T Delta1 and T Delta2 The difference is D1 and D2:

[0063]

[0064] Step 5.2: Divide into five states according to the values ​​of D1 and D2 (state flag: S shift ),in:

[0065] State 1: T Delta1 and T Delta2 All greater than or equal to T min (D1≤0&D2≤0), no phase shift is required in normal state, S shift =1;

[0066] State 2: T Delta1 Less than T min (D1>0), T Delta2 Greater than or equal to T min (D2≤0), use T samp2 The current value obtained by sampling does not require phase shifting, S shift =2;

[0067] State 3: T Delta1 Greater than or equal to T min (D1≤0), T Delta2 Less than T min (D2>0), use T samp1 The current value obtained by sampling does not require phase shifting, S shift =3;

[0068] State 4: T Delta1 and T Delta2 All are smaller than T min And T Delta1 ≥TDelta2 (0<D1≤D2), use T samp1 The sampled current value needs to be phase shifted, S shift =4;

[0069] State 5: T Delta1 and T Delta2 All are smaller than T min And T Delta1 <T Delta2 (0<D2<D1), use T samp2 The sampled current value needs to be phase shifted, S shift =5;

[0070] Step S6: According to the flag bit V Sector and S shift The value of determines the rising trigger threshold point and falling trigger threshold point of the final three-phase PWM in the single rising counting mode, as well as the corresponding sampling time threshold point T samp1 and T samp2 ; The process is as follows:

[0071] Step 6.1: According to the flag bit V Sector and S shift The value of each phase is used to update the starting threshold value of each phase. The calculation formula is as follows:

[0072]

[0073] Among them, T x_upold 、T x_downold (x is a, b, c) is the duty cycle calculated in step S3, the duty cycle is aligned in the center, and the rising trigger threshold point and 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) is 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:

[0074]

[0075] 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. The calculation formula is as follows:

[0076]

[0077] Step S7: According to the flag bit V Sector and S shift , determine which phase of U, V, W the current value is sampled, and reconstruct the three-phase current through the corresponding current observer; the process is as follows:

[0078] Step 7.1: According to the flag bit V Sector and S shift , determine the effective sampling current i x_samp Situation:

[0079]

[0080] Step 7.2: Reconstruct the three-phase current according to the effective sampling current;

[0081] If two-phase currents can be effectively sampled, since the vector sum of the three-phase currents is equal to zero, the third-phase current can be represented by the sampled two-phase currents;

[0082] If only one-phase current can be effectively sampled, the current observer is designed by processing the stator voltage equation of the motor, and the current of the other two phases is estimated using the current of one phase;

[0083] According to the EEMF model, the stator motion equation of the motor is:

[0084]

[0085] Assuming that the a-phase current is available, it is necessary to use the a-phase current alone to ensure the 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. The transformation formula is as follows:

[0086]

[0087] Substitute equation (22) into equation (21), and replace i in equation (21) α 、i β Transform to i a 、i b , after transformation, we get the equation:

[0088]

[0089] in,

[0090] According to equation (23), the a-phase current observer with the abc axis current as the state variable is constructed:

[0091]

[0092] in, is a saturation function. The definition is as follows:

[0093]

[0094] Among them, x is a, b, c, and ξ is the set comparison value;

[0095] In the a-phase current observer, when the state variable Converges to the actual current i of phase a a , the estimated value of the b-axis current will also converge to the actual value; similarly, if only the b-phase current can be sampled, it is necessary to construct the b-phase current observer shown in the following equation (26) for control:

[0096]

[0097] If only the c-phase current can be sampled, the current observer needs to be constructed using the detected c-phase current value for control. Since the vector sum of the three-phase currents is equal to zero, i b Use i a and i c To express it, that is:

[0098] i b =-i a -i c (27)

[0099] Substituting formula (27) into formula (22), we get:

[0100]

[0101] Substituting equation (28) into equation (21), we get:

[0102]

[0103] in,

[0104] According to equation (29), the c-phase current observer with the abc axis current as the state variable is constructed:

[0105]

[0106] In the c-phase current observer, when the state variable Converges to the actual current i of phase c c When , the estimated value of the a-axis current will also converge to the actual value, and the current i is calculated according to formula (27) b The three-phase current is reconstructed from the value of

[0107] At this point, a phase current reconstruction method with single bus current sampling and less phase shifting has been completed. The present invention aligns the corresponding duty ratios of the three phases U, V, and W in different sectors calculated based on the conventional seven-segment SVPWM algorithm and divides them into five states, among which the normal sampling calculation operation segment corresponds to state 1, and directly uses T samp2The current value obtained by sampling is calculated and reconstructed in the corresponding state 2, and T is directly used samp1 The current value obtained by sampling is calculated and reconstructed in the corresponding state 3. After phase shift, T samp1 The current value obtained by sampling is calculated and reconstructed in the corresponding state 4. After phase shift, T samp2 The current value obtained by sampling is calculated and reconstructed in the corresponding state 5. According to the flag bit V Sector and S shift , determine which phase of the current value among U, V, and W is sampled. If only one effective current value can be sampled, the corresponding current observer is designed. The present invention uses a sliding mode observer to reconstruct the three-phase current; as for the use of the same idea to design other types of current observers, it is also within the scope of protection of this patent. The reconstructed three-phase current can be distributed to the U, V, and W three-phase drive control circuit of the motor according to the sector situation, so as to achieve the effect of motor control.

[0108] Finally combined Figure 4 The effectiveness of the phase current reconstruction method with single bus current sampling and less phase shifting of the present invention is illustrated through simulation.

[0109] Simulate in MATLAB, given the system parameters, Table 1 is the system parameter description table.

[0110]

[0111]

[0112] Table 1

[0113] Figure 4 The following is the simulation diagram comparing the actual current and estimated current of the three phases obtained after 1s simulation. 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 per unit (PU) speed setting of the simulation is 0.3 (pu, the same below), and the initial load per unit setting is 0.5 (pu, the same below). At 0.2s, the speed setting is accelerated from 0.3 to 0.6, and the local details are shown in the figure below. Figure 5 As shown in the figure, the motor speed increases. At 0.4s, the load setting is increased from 0.5 to 0.8, and the local details are as follows Figure 6 As shown in the figure, the current amplitude of each phase of the motor increases. At 0.6s, the speed setting is reduced from 0.6 to 0.3, and the local details are as follows Figure 7 As shown in the figure, the motor speed decreases. Finally, at 0.8s, the load setting is reduced from 0.8 to 0.5, and the local details are as follows: Figure 8 As shown, the current amplitude of each phase of the motor becomes smaller.

[0114] In summary, through simulation operation, it can be seen that under the control of a phase current reconstruction method with single bus current sampling and less phase shifting of the present invention, the current observer can keep up with the changes in actual current under different given conditions (acceleration, deceleration, loading, and unloading), and the modified algorithm can achieve the effect of servo motor control.

[0115] The above-described embodiments are only used to illustrate the more specific and detailed embodiments described in this application, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that for ordinary technicians in this field, it is obvious that several modifications and improvements can be made. Modifications or equivalent substitutions of the technical solution of the present invention without departing from the purpose and scope of the technical solution of the present invention should be included in the scope of the claims of the present invention. Therefore, the scope of protection of the patent application should be based on the attached claims.

Claims

1. A phase current reconstruction method with single bus current sampling and less phase shifting, characterized in that: The method comprises the following steps: Step S1: Determine the minimum sampling window time T according to the experimental platform min and sampling delay time T Delay ; Step S2: Based on the seven-segment space vector pulse width modulation SVPWM, calculate the duty ratios of the three phases U, V, and W in different sectors, and assign the sector flag V Sector ; Step S3, according to the calculated duty cycle, align the duty cycle in the center and calculate the rising trigger threshold point and the falling trigger threshold point of the three-phase PWM in the single rising count mode; Step S4: 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 according to the rising trigger threshold point and the falling trigger threshold point of the three-phase PWM. Delta1 , and the rising trigger threshold difference value T between the minimum duty cycle phase and the middle duty cycle phase Delta2 ; Step S5: calculate the rising trigger threshold value difference T Delta1 and T Delta2 Respectively with the minimum sampling window time T min Compare and assign flag bit S shift ; Step S6: According to the flag bit V Sector and S shift The value of determines the rising trigger threshold point and falling trigger threshold point of the final three-phase PWM in the single rising counting mode, as well as the corresponding sampling time threshold point T samp1 and T samp2 ; Step S7: According to the flag bit V Sector and S shift , determine which phase of U, V, and W the current value is sampled, and reconstruct the three-phase current through the corresponding current observer.

2. A phase current reconstruction method with single bus current sampling and less phase shifting according to claim 1, characterized in that: In step S5, T is calculated respectively. min With T Delta1 and T Delta2 The difference between D1 and D2 is used to obtain five states, and the flag bit S is assigned shift : State 1: Normal state does not require phase shifting, S shift =1; State 2: Using T samp2 The current value obtained by sampling does not require phase shifting, S shift =2; State 3: Using T samp1 The current value obtained by sampling does not require phase shifting, S shift =3; State 4: Using T samp1 The sampled current value needs to be phase shifted, S shift =4; State 5: Using T samp2 The sampled current value needs to be phase shifted, S shift =5.

3. A phase current reconstruction method with single bus current sampling and less phase shifting according to claim 1 or 2, characterized in that: In step S6, according to the flag bit V Sector and S shift The value of is discussed by classification. When phase shift is not required, the starting threshold point remains unchanged. If phase shift is required, corresponding changes are made to determine the rising trigger threshold point and falling trigger threshold point of the final three-phase PWM in single rising count mode. The calculation formula for phase a is as follows: Among them, T a_upold , T a_downold The duty cycle calculated in step S3 is aligned in the center, 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 a_up , T a_down are 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:

4. The phase current reconstruction method with single bus current sampling and less phase shifting according to claim 3 is characterized in that: In step S7, according to the flag bit V Sector and S shift , determine which phase of U, V, W the current value is sampled from, and reconstruct the calculation process of the three-phase current through the corresponding current observer as follows: According to the EEMF mathematical model, the stator motion equation of the motor is: Taking phase a as an example, assuming that the current of phase a is available, the current of phase a needs to be used alone 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 system to the natural coordinate system abc axis system. The transformation formula is as follows: Substitute equation (5) into equation (4), and replace i in equation (4) α 、i β Transform to i a 、i b , after transformation, we get the equation: in, According to equation (6), the a phase sliding mode current observer with the abc axis current as the state variable is constructed: in, is a saturation function. The definition is as follows: Among them, x is a, b, c, and ξ is the set comparison value; In the a-phase current observer, when the state variable Converges to the actual current i of phase a a When , the estimated value of the b-axis current will also converge to the actual value; similarly, if only the b-phase current can be sampled, it is necessary to construct a current observer based on the detected b-phase current value for control; If only the c-phase current can be sampled, the current observer needs to be constructed using the detected c-phase current value for control. Since the vector sum of the three-phase currents is equal to zero, i b You can use a and i c To express, that is i b =-i a -i c (9) Substitute equation (9) into equation (5), and then into equation (4) to obtain the c-phase current observer after rearrangement and transformation. When the state variable Converges to the actual current i of phase c c When , the estimated value of the a-axis current will also converge to the actual value, and the current i is calculated according to formula (9): b The three-phase current is reconstructed from the value of

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