A low-noise phase current reconstruction method based on single-resistor current sampling

Abstract

The present invention relates to the field of motor control and discloses a low-noise phase current reconstruction method based on single-resistor current sampling, comprising the following steps: duty cycle shifting and current sampling point setting: obtaining the times of the three-phase output high level in the current cycle as Ta, Tb, and Tc, sorting these three times from largest to smallest as Tmax, Tmid, and Tmin, with T1 = Tmax-Tmid and T2 = Tmid-Tmin, and the minimum time required for sampling as Tsample; when T1 and T2 are both less than Tsample, the system is located in the third unsampling region; when T1 is less than Tsample and T2 is greater than Tsample, the system is located in the second unsampling region; when T2 is less than Tsample and T1 is greater than Tsample, the system is located in the first unsampling region; when T1 and T2 are both greater than or equal to Tsample, two currents are directly obtained in the sampleable region, and only one phase current needs to be sampled in the unsampling region, and finally the other two phases are calculated using the one phase current. The present invention can greatly expand the single-resistor sampling region and reduce the current sampling window increased by current sampling, thereby greatly reducing the electromagnetic noise of the single-resistor solution, and the solution is very simple to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a low-noise phase current reconstruction method based on single-resistor current sampling. Background Art

[0002] Permanent magnet synchronous motors (PMSMs) are widely used in household products due to their high efficiency and energy-saving advantages. To further reduce system costs, single-resistor sampling solutions have attracted widespread attention. However, using single-resistor sampling also has some adverse effects, such as phase current reconstruction and noise. While phase current reconstruction has been extensively explored in the literature, the noise issues associated with single-resistor solutions have rarely been addressed.

[0003] The root cause of noise issues with single-resistor sampling schemes stems from electromagnetic noise introduced by the sampling window. Since the signal buildup and stabilization of the current sampling circuit and the sampling by the microcontroller require time, a minimum sampling window exists regardless of the current reconstruction method used. Given a fixed minimum sampling window, a common approach to reducing noise issues with single-resistor sampling schemes is to reduce the sampling ratio. Specifically, sampling is performed once, and, assuming an ideal system, the duty cycle is calculated and output for N cycles. This effectively reduces the noise associated with single-resistor sampling schemes by maintaining the sampling window only during the cycles requiring current sampling and maintaining normal output during the remaining cycles. However, this reduction in the sampling ratio has a limit: beyond a certain point, the accumulation of errors will ultimately lead to system failure.

[0004] In order to solve the noise problem of the single resistor sampling solution, the present invention proposes a new current reconstruction method, which can significantly reduce the electromagnetic noise caused by the sampling window, while avoiding the system crash problem caused by error accumulation caused by the method of reducing the sampling ratio. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides a low-noise phase current reconstruction method based on single-resistor current sampling.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-noise phase current reconstruction method based on single-resistor current sampling, comprising the following steps:

[0007] Duty cycle movement and current sampling point setting:

[0008] Get the time of the three-phase output high level in the current cycle as Ta, Tb, and Tc, and sort these three times from large to small as Tmax, Tmid, and Tmin, and record T1 = Tmax-Tmid, T2 = Tmid-Tmin, and record the minimum time required for sampling as Tsample;

[0009] When T1 and T2 are both smaller than Tsample, it is located in the unsampling area 3;

[0010] When T1 is less than Tsample and T2 is greater than Tsample, it is located in the unsampling area 2;

[0011] When T2 is less than Tsample and T1 is greater than Tsample, it is located in the unsampling area 1;

[0012] When T1 and T2 are both greater than or equal to Tsample, they are in the sampleable area and two currents are directly sampled;

[0013] Sampling strategy in non-sampling areas:

[0014] When it is in the non-sampling area 1, the duty cycle does not need to be moved, and current sampling is performed only in T1. Although T2 is smaller than Tsample, current sampling is not performed.

[0015] When in the second non-sampling area, there is no need to shift the duty cycle, and current sampling is performed only in T2. Although T1 is smaller than Tsample, current sampling is not performed.

[0016] When in the unsampling area 3, the size of T1 and T2 is determined: if T1 is greater than T2, the duty cycle is shifted, and current sampling is performed only in T1, and no current sampling is required in T2; if T2 is greater than T1, the duty cycle is shifted, and current sampling is performed only in T2, and no current sampling is required in T1;

[0017] The other two phase currents are obtained based on the one phase current collected in the non-sampling area.

[0018] Preferably, the step of obtaining the other two-phase currents according to one-phase current is as follows:

[0019] Using three-phase current observer:

[0020]

[0021]

[0022] in is the observed state variable of a simple sine wave, They are The differential expression of D1a, D1b, D1c, D2a, D2b, D2c is the feedback constant, ω is the electrical angular velocity of the phase current, e a 、e b 、e c Represent the measurement and estimation errors of the three-phase currents a, b, and c respectively;

[0023] Let ε1=D1a*e a +D1b*e b +D1c*e c 、ε2=D2a*e a +D2b*e b +D2c*e c (3)

[0024] When in the unobservable region, there is only one phase current at a time. Here we first consider the case where the current is phase a, that is,

[0025] e b =e c =0 (4)

[0026] but

[0027]

[0028] in:

[0029] Then formula (5) can be further obtained:

[0030]

[0031] According to the basic principle of state space equation, when When the eigenvalues of have negative real parts, the error ε will converge to 0 and the system is stable;

[0032] Let the system pole be located at -3ω, we can get

[0033] Similarly, we can get:

[0034] Preferably, the input unit includes inputs of a one-way system and a three-phase system, the air switch includes a two-phase circuit breaker and a three-phase circuit breaker, and a mechanical interlocking switch is used to achieve interlocking to prevent the input unit from short-circuiting.

[0035] Preferably, Tsample includes a dead time and a sampling current stabilization time.

[0036] In traditional single-resistor solutions, the duty cycle of unsampling zones 1, 2, and 3 all need to be adjusted to create a minimum sampling window. However, the single-resistor solution of the present invention only has unsampling zone 3, and the sampling window in sampling zone 3 is also reduced by half. Therefore, this method can greatly expand the single-resistor sampling area and reduce the current sampling window increased by current sampling, thereby greatly reducing the electromagnetic noise of the single-resistor solution. The solution is also very simple to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a three-phase driving and sampling circuit.

[0038] Figure 2 It is the sampleable and non-sampleable areas divided according to SVPWM (taking sector 1 as an example, phase A outputs high level time for the longest time, phase B is second, and phase C is the smallest).

[0039] Figure 3 The traditional sampling method of the unsampling area is compared with the method of the present invention.

[0040] Figure 4 It is a three-phase current observer based on single-phase current.

[0041] Figure 5 It is a comparison of the sampling areas of the traditional sampling method and the method of the present invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0043] Please refer to the attached figure for a low-noise phase current reconstruction method based on single-resistor current sampling, duty cycle shift and current sampling point setting, and the obtained current is handed over to step 2:

[0044] The time for obtaining the high level of the three-phase output of the current cycle is Ta, Tb, and Tc, and these three times are sorted from large to small as Tmax, Tmid, and Tmin, and T1 = Tmax-Tmid, T2 = Tmid-Tmin, and the minimum time required for sampling is Tsample (this time includes the dead time and the sampling current stabilization time). When T1 and T2 are both less than Tsample, it is in the unobservable area 3; when T1 is less than Tsample and T2 is greater than Tsample, it is in the unsampling area 2; when T2 is less than Tsample and T1 is greater than Tsample, it is in the unsampling area 1; when T1 and T2 are both greater than or equal to Tsample, it is in the sampleable area. The division of these areas is as follows Figure 2 shown.

[0045] When it is in the sampleable area, no operation is required and two currents can be directly sampled and obtained.

[0046] Sampling strategies in non-sampling areas are as follows: Figure 3 shown

[0047] When in the non-sampling area 1, there is no need to shift the duty cycle, and current sampling is performed only in T1. Although T2 is smaller than Tsample, current sampling is not performed.

[0048] When it is in the non-sampling area 2, there is no need to move the duty cycle, and current sampling is performed only in T2. Although T1 is smaller than Tsample, current sampling is not performed.

[0049] When in the unsampling area 3, the sizes of T1 and T2 are determined: if T1 is greater than T2, the duty cycle is shifted, and current sampling is performed only in T1, and no current sampling is required in T2; if T2 is greater than T1, the duty cycle is shifted, and current sampling is performed only in T2, and no current sampling is required in T1.

[0050] 2) Current reconstruction

[0051] For traditional single-resistor sampling schemes, at least two phase currents need to be collected, and the third phase current needs to be calculated based on the basic conclusion that the sum of the three-phase currents is zero. Finally, the duty cycle is controlled based on the sampling results of the three-phase currents. However, the current collection results in step 1 of the present invention only collect one phase current in the unsampling area. In order to obtain the other two phase currents, the present invention uses a three-phase current observer to obtain the other two phase currents. Unlike the method of reducing the current sampling ratio introduced in the background technology, the three-phase current observer uses the collected phase current to update the observation value in each cycle, thereby avoiding the system crash problem caused by error accumulation.

[0052] Three-phase current observer:

[0053]

[0054]

[0055] in is the observed state variable of a simple sine wave, They are The differential expression of D1a, D1b, D1c, D2a, D2b, D2c is the feedback constant, ω is the electrical angular velocity of the phase current, e a 、e b 、e c Represent the measurement and estimation errors of the three-phase currents a, b, and c respectively.

[0056] Let ε1=D1a*e a +D1b*e b +D1c*e c 、ε2=D2a*e a +D2b*e b +D2c*e c (3)

[0057] When in the unobservable region, there is only one phase current at a time. Here we first consider the case where the current is phase a, that is,

[0058] e b =e c =0 (4)

[0059] but

[0060]

[0061] in:

[0062] Then formula (5) can be further obtained:

[0063]

[0064] According to the basic principle of state space equation, when When the eigenvalues of have negative real parts, the error ε will converge to 0 and the system is stable.

[0065] Let the system pole be located at -3ω, we can get

[0066] Similarly, we can get:

[0067] For specific control block diagram, please refer to Figure 4 .

[0068] 3) Current processing

[0069] When it is in the sampleable region, the directly sampled current is used; when it is in the unsampleable region, the estimated results of the three-phase current observer are used.

[0070] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A low-noise phase current reconstruction method based on single-resistor current sampling, characterized in that: The steps include: Duty cycle movement and current sampling point setting: Get the time of the three-phase output high level in the current cycle as Ta, Tb, and Tc, and sort these three times from large to small as Tmax, Tmid, and Tmin, and record T1 = Tmax-Tmid, T2 = Tmid-Tmin, and record the minimum time required for sampling as Tsample; When T1 and T2 are both smaller than Tsample, it is located in the unsampling area 3; When T1 is less than Tsample and T2 is greater than Tsample, it is located in the unsampling area 2; When T2 is less than Tsample and T1 is greater than Tsample, it is located in the unsampling area 1; When T1 and T2 are both greater than or equal to Tsample, they are in the sampleable area and two currents are directly sampled; Sampling strategy in non-sampling areas: When it is in the non-sampling area 1, there is no need to move the duty cycle, and current sampling is only performed in T1. Although T2 is smaller than Tsample, current sampling is not performed. When it is in the second non-sampling area, there is no need to move the duty cycle, and current sampling is only performed in T2. Although T1 is less than Tsample, current sampling is not performed; When in the unsampling area 3, the size of T1 and T2 is determined: if T1 is greater than T2, the duty cycle is shifted and current sampling is performed only in T1, and no current sampling is required in T2; If T2 is greater than T1, the duty cycle is shifted and current sampling is performed only in T2, and no current sampling is required in T1; The other two phase currents are obtained based on the one phase current collected in the non-sampling area.

2. A low-noise phase current reconstruction method based on single-resistor current sampling according to claim 1, characterized in that: Steps to obtain the other two phase currents based on one phase current: Using three-phase current observer: in is the observed state variable of a simple sine wave, They are The differential expression of D1a, D1b, D1c, D2a, D2b, D2c is the feedback constant, ω is the electrical angular velocity of the phase current, e a 、e b 、e c Represent the measurement and estimation errors of the three-phase currents a, b, and c respectively; Let ε1 = D1a * ea + D1b * e b + D1c * e c and ε2 = D2a * e a + D2b * e b + D2c * e c (3) When in the unobservable region, there is only one phase current at a time. Here we first consider the case where the current is phase a, that is, And b =and c =0 (4) but in: Then formula (5) can be further obtained: According to the basic principle of state space equation, when When the eigenvalues of have negative real parts, the error ε will converge to 0 and the system is stable; Let the system pole be located at -3ω, we can get Similarly, we can get:

3. The low-noise phase current reconstruction method based on single-resistor current sampling according to claim 1, characterized in that: Tsample includes the dead time and the sampling current stabilization time.

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