A two-level direct torque control method to eliminate zero vector common mode voltage spikes

Abstract

The present invention relates to a two-level direct torque control method capable of eliminating zero vector common mode voltage spikes. The method establishes a voltage vector correction table for two-level direct torque control according to the changing values ​​of the output values ​​of the torque and flux hysteresis comparator and the changing values ​​of the stator flux sector number of the motor, obtains the voltage vector correction value by querying the voltage vector correction table, and uses the correction value to perform correction in the process of querying the traditional switch table of the two-level direct torque control. The corrected voltage vector can ensure that no zero vector is generated during the commutation process. Compared with the traditional two-level direct torque control, the present invention can effectively eliminate the common mode voltage spike; at the same time, compared with other methods for eliminating the common mode voltage spike, the present invention can retain the simple control structure and good control performance of the traditional direct torque control.

Description

Technical Field

[0001] The invention relates to the field of motor drive control, and in particular to a two-level direct torque control method capable of eliminating zero vector common mode voltage spikes. Background Art

[0002] The common-mode voltage generated by the two-level inverter during operation not only causes damage to the motor bearings, but also causes the misoperation of the motor protection measures and generates negative effects such as electromagnetic interference. Therefore, effective measures must be taken to suppress it. The voltage vector of the two-level inverter includes a zero vector and six evenly distributed effective vectors. The common-mode voltage amplitude generated by the zero vector is three times that of the effective vector. Therefore, the traditional direct torque control strategy can significantly suppress the common-mode voltage by abandoning the zero vector and storing only the effective vector in the switch table. However, due to the influence of the inverter dead zone effect, the zero vector is still generated during the inverter commutation process, thereby forming a common-mode voltage spike.

[0003] The study found that when the inverter switches between adjacent effective vectors (angle 60°) or between opposite effective vectors (angle 180°), no zero vector will be generated. Zero vector will only be generated when switching between vectors with an angle of 120°. Therefore, as long as the switching between vectors with an angle of 120° is avoided, the common-mode voltage spike can be eliminated. The existing modulation strategy can avoid switching between vectors with an angle of 120° by changing the carrier or voltage comparison value, and the existing predictive control can avoid switching between vectors with an angle of 120° by vector pre-screening, thereby achieving the purpose of eliminating the common-mode voltage spike. However, the above method cannot be applied to the direct torque control strategy based on the switch table, so the existing direct torque control strategy cannot eliminate the common-mode voltage spike. Summary of the invention

[0004] Based on this, it is necessary to provide a new direct torque control strategy for the above-mentioned problem, by correcting the query process of the two-level direct torque control switch table to avoid switching between vectors with an angle of 120°, thereby ensuring that no zero vector is generated during the commutation process and eliminating common-mode voltage spikes. The present invention provides a two-level direct torque control method capable of eliminating zero vector common-mode voltage spikes, comprising:

[0005] Obtain the torque and flux hysteresis comparator output values ​​and the motor stator flux sector number, and query the traditional voltage vector switch table of two-level direct torque control to determine the primary position of the required voltage vector in the switch table;

[0006] Obtain the changing values ​​of the torque and flux hysteresis comparator output values ​​and the changing values ​​of the motor stator flux sector number, and query the voltage vector correction table of the two-level direct torque control to obtain the voltage vector correction value from the corresponding position in the correction table;

[0007] The initial position of the required voltage vector in the switch table is corrected according to the voltage vector correction value to obtain a final position, a voltage vector is obtained from the final position, and the voltage vector is used to drive the motor.

[0008] Preferably, the torque hysteresis comparator output value progressive value τ T Reflects the torque hysteresis comparator output value H T The change of τ T =0 represents H T Keep 0 unchanged, τ T =1 represents H T From 0 to 1, τ T =2 represents H T From 1 to 0, τ T =3 represents H T Keep 1 unchanged;

[0009] The variable value τ of the output value of the flux hysteresis comparator Ψ Reflects the output value H of the magnetic hysteresis comparator Ψ The change of τ Ψ =0 represents H Ψ Keep 0 unchanged, τ Ψ =1 represents H Ψ From 0 to 1, τ Ψ =2 represents H Ψ From 1 to 0, τ Ψ =3 represents H Ψ Keep 1 unchanged;

[0010] The stator flux sector variation value τ S Reflects the motor stator flux sector number H S The change of τ S =0 represents H S Keep unchanged, τ S =1 represents H S Positive change, τ S =2 represents H S Negative changes.

[0011] Preferably, the voltage vector correction value T in the voltage vector correction table of the two-level direct torque control r The value of τ S The value of is determined in three situations:

[0012] Among them, when τ S =0, T r The value of τ is determined by T , τ Ψ The value combination of τ is determined: T =1, τ Ψ =0 or τ T=2, τ Ψ =3, T r The value of is 1; when τ T =1, τ Ψ =3 or τ T =2, τ Ψ =0, T r The value of is -1; when τ T , τ Ψ For other value combinations, T r The value of is 0;

[0013] When τ S =1, T r The value of τ is determined by T , τ Ψ The value combination of τ is determined: T =1, τ Ψ =1 or τ T =1, τ Ψ =2 or τ T =2, τ Ψ =1 or τ T =2, τ Ψ =2, T r The value of is 1; when τ T =0, τ Ψ =1 or τ T =3, τ Ψ =2, T r The value of is -1; when τ T , τ Ψ For other value combinations, T r The value of is 0;

[0014] When τ S =2, T r The value of τ is determined by T , τ Ψ The value combination is determined: when τ T =1, τ Ψ =1 or τ T =1, τ Ψ =2 or τ T =2, τ Ψ =1 or τ T =2, τ Ψ =2, T r The value of is -1; when τ T =0, τ Ψ =2 or τ T =3, τ Ψ =1, T r The value of is 1; when τ T , τ Ψ For other value combinations, T r The value of is 0;

[0015] The voltage vector correction table for two-level direct torque control is established through the above process.

[0016] Preferably, the voltage vector correction value T r The method of correcting the initial position of the required voltage vector in the switch table is to change the stator flux sector number H S Replace with H S +T r , that is: when T r =1, the stator flux sector number corresponding to the initial position in the switch table is changed by 1 grid in the positive direction to obtain the final position; when T r = -1, the stator flux sector number corresponding to the initial position in the switch table is changed negatively by 1 grid to obtain the final position; when T r =0, the final selection position is the initial selection position.

[0017] Compared with the prior art, the present invention retains the advantages of the simplicity of the direct torque control algorithm and good steady-state and dynamic performance while eliminating the common-mode voltage spike. That is, compared with the traditional two-level direct torque control, the present invention innovatively proposes to establish a voltage vector correction table for the two-level direct torque control, avoiding the situation of generating a zero vector during the inverter commutation process, thereby eliminating the common-mode voltage spike; compared with other methods for eliminating common-mode voltage spikes, such as improved modulation strategies or predictive control strategies, the present invention can be applied to the general environment of the direct torque control strategy, which can retain the advantages of direct torque control, and the advantages include simple structure, good dynamic performance, strong parameter robustness, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of the two-level inverter-motor system used in the present invention;

[0019] Figure 2 Schematic diagram of effective vector of two-level inverter used in the present invention;

[0020] Figure 3 A schematic diagram of a case of a table lookup correction process in the implementation of the present invention;

[0021] Figure 4 It is a schematic diagram of the implementation process of the present invention;

[0022] Figure 5 Schematic diagram of the structure of a torque hysteresis comparator and a flux hysteresis comparator in one embodiment of the present invention;

[0023] Figure 6 It is a common mode voltage waveform diagram of the conventional direct torque control method and the direct torque control method of the present invention under the condition of a motor speed of 400r / min;

[0024] Figure 7 It is a transient comparison test waveform diagram of the traditional direct torque control method and the direct torque control method of the present invention. DETAILED DESCRIPTION

[0025] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0027] The present invention provides a technical solution: a two-level direct torque control method capable of eliminating zero vector common mode voltage spikes, comprising:

[0028] Obtain the torque and flux hysteresis comparator output values ​​and the motor stator flux sector number, and query the traditional voltage vector switch table of two-level direct torque control to determine the primary position of the required voltage vector in the switch table;

[0029] Obtain the changing values ​​of the torque and flux hysteresis comparator output values ​​and the changing values ​​of the motor stator flux sector number, and query the voltage vector correction table of the two-level direct torque control to obtain the voltage vector correction value from the corresponding position in the correction table;

[0030] The initial position of the required voltage vector in the switch table is corrected according to the voltage vector correction value to obtain a final position, a voltage vector is obtained from the final position, and the voltage vector is used to drive the motor.

[0031] Specifically, the conventional vector switch table of the two-level direct torque control is shown in Table 1:

[0032]

[0033]

[0034] Table 1

[0035] Among them, the torque hysteresis comparator output value H T , the output value of the flux hysteresis comparator H ψ , stator flux sector number H S, two-level inverter effective vector V1~V6;

[0036] Specifically, the torque hysteresis comparator output value τ T Reflects the torque hysteresis comparator output value H T The changes of τ T =0 represents H T Keep 0 unchanged, τ T =1 represents H T From 0 to 1, τ T =2 represents H T From 1 to 0, τ T =3 represents H T Keep 1 unchanged;

[0037] The variable value τ of the output value of the flux hysteresis comparator Ψ Reflects the output value H of the magnetic hysteresis comparator Ψ The changes of τ Ψ =0 represents H Ψ Keep 0 unchanged, τ Ψ =1 represents H Ψ From 0 to 1, τ Ψ =2 represents H Ψ From 1 to 0, τ Ψ =3 represents H Ψ Keep 1 unchanged;

[0038] The stator flux sector variation value τ S Reflects the motor stator flux sector number H S The changes of τ S =0 represents H S Remain unchanged; τ S =1 represents H S Positive changes, including H S From 1 to 2 or from 2 to 3 or from 3 to 4 or from 4 to 5 or from 5 to 6 or from 6 to 1, τ S =2 represents H S Negative changes, including H S From 6 to 5 or from 5 to 4 or from 4 to 3 or from 3 to 2 or from 2 to 1 or from 1 to 6.

[0039] Specifically, the voltage vector correction value T in the voltage vector correction table of the two-level direct torque control is r The value of τ S The value of is determined in three cases:

[0040] Among them, when τ S =0, T r The value of τ is determined by T , τΨ The value combination of τ is determined: T =1, τ Ψ =0 or τ T =2, τ Ψ =3, T r The value of is 1; when τ T =1, τ Ψ =3 or τ T =2, τ Ψ =0, T r The value of is -1; when τ T , τ Ψ For other value combinations, T r The value of is 0;

[0041] When τ S =1, T r The value of τ is determined by T , τ Ψ The value combination of τ is determined: T =1, τ Ψ =1 or τ T =1, τ Ψ =2 or τ T =2, τ Ψ =1 or τ T =2, τ Ψ =2, T r The value of is 1; when τ T =0, τ Ψ =1 or τ T =3, τ Ψ =2, T r The value of is -1; when τ T , τ Ψ For other value combinations, T r The value of is 0;

[0042] When τ S =2, T r The value of τ is determined by T , τ Ψ The value combination is determined: when τ T =1, τ Ψ =1 or τ T =1, τ Ψ =2 or τ T =2, τ Ψ =1 or τ T =2, τ Ψ =2, T r The value of is -1; when τ T =0, τ Ψ =2 or τ T =3, τ Ψ =1, Tr The value of is 1; when τ T , τ Ψ For other value combinations, T r The value of is 0;

[0043] The voltage vector correction table of two-level direct torque control is established by the above process, as shown in Table 2:

[0044]

[0045] Table 2

[0046] Specifically, the voltage vector correction value T r The method of correcting the initial position of the required voltage vector in the switch table is to change the stator flux sector number H S Replace with H S +T r , that is: when T r =1, the stator flux sector number corresponding to the initial position in the switch table is changed positively by 1 grid to obtain the final position, including changing from 1 to 2 or from 2 to 3 or from 3 to 4 or from 4 to 5 or from 5 to 6 or from 6 to 1; when T r = -1, the stator flux sector number corresponding to the initial position in the switch table is changed negatively by 1 grid to obtain the final position, including from 6 to 5 or from 5 to 4 or from 4 to 3 or from 3 to 2 or from 2 to 1 or from 1 to 6; when T r =0, the final selection position is the initial selection position.

[0047] Specifically, the selected voltage vector is used to drive the motor in the following manner: according to the voltage vector and the switch device state correspondence table (Table 3), a drive level signal is output to each switch device of the inverter:

[0048]

[0049] Table 3

[0050] Among them, 1 represents that the state of the switch device is on, and 0 represents that the state of the switch device is off.

[0051] An example is given to illustrate the table lookup correction process: Assume that the stator flux sector number H in the previous control cycle S =1, torque hysteresis comparator output value H T =0, magnetic hysteresis comparator H Ψ =1, according to Table 1, the vector selected in the previous control cycle is V6; assuming that the current cycle H S Increase to 2, H T becomes 1, H Ψ becomes 0, and the vector at the initial position is V4 according to Table 1, and the angle between it and V6 is 120°;S The value of changes positively, so τ S =1,H T The value of changes from 0 to 1, so τ T =1,H Ψ The value of changes from 1 to 0, so τ Ψ =2, query table 2 to get T r The value is 1; according to the correction principle, the stator flux sector number is corrected to 3, and the vector at the final position after correction is V5, such as Figure 3 shown.

[0052] The present invention is further described in detail below with reference to specific examples and drawings. Figure 4 The present invention is implemented as a flow chart, and the implementation method of the present invention comprises the following steps:

[0053] (1) Calculate the stator flux amplitude |ψ s |、Stator flux sector number H S , electromagnetic torque T e .

[0054] Calculate the two-phase stationary coordinate system components i of the stator current α 、i β . Detect the three-phase current i of the motor stator A 、i B 、i C , transform it into the two-phase stationary coordinate system component i α 、i β The formula is as follows:

[0055]

[0056] Calculate the two-phase stationary coordinate system components u of the stator voltage α 、u β . Detect the DC voltage u on the inverter input side dc , and calculate the two-phase stationary coordinate system component u of the stator three-phase voltage according to the state of the three-phase switch device α 、u β The formula is as follows:

[0057]

[0058] Calculate the two-phase stationary coordinate system component ψ of the stator flux α , β The formula is as follows:

[0059] ψ α =∫(u α -R s i α )dt

[0060] ψ β =∫(uβ -R s i β )dt

[0061] In the formula, R s is the stator resistance.

[0062] Calculate the stator flux amplitude |ψ s |、Phase angle θ Ψ The formula is as follows:

[0063]

[0064]

[0065] Calculate the stator flux sector number H S The formula is as follows:

[0066]

[0067] Calculate the electromagnetic torque T e The formula is as follows:

[0068]

[0069] Where p is the number of motor pole pairs.

[0070] (2) Obtain the output value H of the torque hysteresis comparator and the flux hysteresis comparator T , H Ψ .H T The value 1 and 0 represent increasing torque and decreasing torque respectively. Ψ The value 1 and 0 represent increasing the flux and decreasing the flux respectively. Figure 5 As shown in Figure B T , B Ψ They are torque and magnetic link width respectively, and B is generally taken T 0.5% to 5% times the rated torque, B Ψ It is 0.1% to 2% times the permanent magnet flux. e ,Δ|ψ s | are torque error and flux error respectively, and the calculation formula is as follows:

[0071] ΔT e =T e * -T e

[0072] Δ|ψ s |=|ψ s | * -|ψ s |

[0073] Where, Te * and |ψ s | * They are the torque reference value and the stator flux amplitude reference value respectively.

[0074] (3) According to the output H of the hysteresis comparator T , H Ψ And stator flux sector number H S The conventional voltage vector switch table of two-level direct torque control is queried to determine the primary position of the required voltage vector in the switch table.

[0075] (4) Obtain the changing value τ of the torque and flux hysteresis comparator output value T , τ Ψ And the variable value τ of the motor stator flux sector number S According to H T , H Ψ , H S The values ​​of the previous control cycle and the current control cycle are respectively obtained as the progressive value τ T , τ Ψ , τ S , the corresponding relationship is as follows:

[0076]

[0077]

[0078]

[0079] (5) According to τ T , τ Ψ , τ S Query the voltage vector correction table of two-level direct torque control to obtain the voltage vector correction value T r .

[0080] (6) Based on the voltage vector correction value T r Correct the initial position of the required voltage vector in the switch table by changing the stator flux sector number H S Replace with H S +T r , and obtain the final selected position in the switch table.

[0081] (7) A voltage vector is obtained from the final selection position in the switch table, and a corresponding drive signal level is output to the inverter switch device according to the corresponding relationship table between the voltage vector and the switch device state, thereby driving the motor.

[0082] A two-level direct torque control method for eliminating zero-vector common-mode voltage spikes has been experimentally verified on a 1.6kW permanent magnet synchronous motor drive system. The system has good dynamic and static performances, and the common-mode voltage spikes are effectively suppressed.

[0083] The common mode voltage waveforms of the DTC of the present invention and the traditional DTC in steady state are as follows: Figure 6 As shown in the figure. The test conditions are motor speed 400r / min, load torque 7.5N·m. Among them, (a) is the common mode voltage waveform under the traditional DTC method, and (b) is the common mode voltage waveform under the DTC method of the present invention. Comparing the waveforms in the figure, it can be seen that the common mode voltage waveform of the traditional method has obvious peaks, and the method of the present invention effectively eliminates the common mode voltage spikes.

[0084] The transient comparison test waveforms of the DTC of the present invention and the traditional DTC are as follows: Figure 7 As shown. The test condition is that the motor speed is stepped from 400r / min to -400r / min, and then stepped back to 400r / min after 1 second. Among them, (a) is the electromagnetic torque, speed and motor A phase current waveform under the traditional DTC method, and (b) is the electromagnetic torque, speed and motor A phase current waveform under the DTC method of the present invention. It can be seen from the figure that the DTC method of the present invention inherits the characteristic of fast torque response speed of the traditional DTC method.

[0085] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0086] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A two-level direct torque control method capable of eliminating zero vector common mode voltage spikes, characterized in that: include: Step 1: Calculate the stator flux amplitude |ψ s |、Stator flux sector number H S , electromagnetic torque T e ; Step 2: Get the output value H of the torque hysteresis comparator T , the output value H of the flux hysteresis comparator Ψ ; Step 3: According to the output H of the torque hysteresis comparator T , the output value H of the flux hysteresis comparator Ψ And stator flux sector number H S Query the conventional voltage vector switch table of two-level direct torque control to determine the primary position of the required voltage vector in the switch table; Step 4: Obtain the changing value τ of the torque hysteresis comparator output value T , the output value of the flux hysteresis comparator τ Ψ And the variable value τ of the motor stator flux sector number S ; Step 5: According to the changing value τ of the torque hysteresis comparator output value T , the output value of the flux hysteresis comparator τ Ψ , the changing value τ of the motor stator flux sector number S Query the voltage vector correction table of two-level direct torque control to obtain the voltage vector correction value T r ; Step 6: Correct the value T according to the voltage vector r Correct the initial position of the required voltage vector in the switch table by changing the stator flux sector number H S Replace with H S +T r , get the final selected position in the switch table; Step 7: Obtain a voltage vector at the final selection position in the switch table, and output a corresponding drive signal level to the inverter switch device according to the voltage vector and switch device state correspondence table, thereby driving the motor.

2. The method according to claim 1, characterized in that The torque hysteresis comparator output value τ T Reflects the torque hysteresis comparator output value H T The change of τ T =0 represents H T Keep 0 unchanged, τ T =1 represents H T From 0 to 1, τ T =2 represents H T From 1 to 0, τ T =3 represents H T Keep 1 unchanged; The variable value τ of the output value of the flux hysteresis comparator Ψ Reflects the output value H of the magnetic hysteresis comparator Ψ The change of τ Ψ =0 represents H Ψ Keep 0 unchanged, τ Ψ =1 represents H Ψ From 0 to 1, τ Ψ =2 represents H Ψ From 1 to 0, τ Ψ =3 represents H Ψ Keep 1 unchanged; The stator flux sector variation value τ S Reflects the motor stator flux sector number H S The change of τ S =0 represents H S Keep unchanged, τ S =1 represents H S Positive change, τ S =2 represents H S Negative changes.

3. The method according to claim 1, characterized in that The voltage vector correction value T in the voltage vector correction table of the two-level direct torque control r The value of τ S The value of is divided into the following three cases: The first case: τ S =0, under this condition, T r The value of τ is determined by T , τ Ψ The value combination of is determined: when τ T =1, τ Ψ =0 or τ T =2, τ Ψ =3, T r The value of is 1; when τ T =1, τ Ψ =3 or τ T =2, τ Ψ =0, T r The value of is -1; when τ T , τ Ψ For other value combinations, T r The value of is 0; The second case: τ S =1, under this condition, T r The value of τ is determined by T , τ Ψ The value combination of is determined: when τ T =1, τ Ψ =1 or τ T =1, τ Ψ =2 or τ T =2, τ Ψ =1 or τ T =2, τ Ψ =2, T r The value of is 1; when τ T =0, τ Ψ =1 or τ T =3, τ Ψ =2, T r The value of is -1; when τ T , τ Ψ For other value combinations, T r The value of is 0; The third case: τ S =2, under this condition, T r The value of τ is determined by T , τ Ψ The value combination is determined: when τ T =1, τ Ψ =1 or τ T =1, τ Ψ =2 or τ T =2, τ Ψ =1 or τ T =2, τ Ψ =2, T r The value of is -1; when τ T =0, τ Ψ =2 or τ T =3, τ Ψ =1, T r The value of is 1; when τ T , τ Ψ For other value combinations, T r The value of is 0; The voltage vector correction table for two-level direct torque control is established through the above process.

4. The method according to claim 1, characterized in that: According to the voltage vector correction value T r The method of correcting the initial position of the required voltage vector in the switch table is to change the stator flux sector number H S Replace with H S +T r , that is: when T r =1, the stator flux sector number corresponding to the initial position in the switch table is changed by 1 grid in the positive direction to obtain the final position; when T r = -1, the stator flux sector number corresponding to the initial position in the switch table is changed negatively by 1 grid to obtain the final position; when T r =0, the final selection position is the initial selection position.

5. The method according to claim 1, characterized in that Torque hysteresis comparator H T The values ​​1 and 0 represent increasing torque and decreasing torque respectively; the output value H of the flux hysteresis comparator Ψ The values ​​1 and 0 represent increasing the magnetic flux and decreasing the magnetic flux respectively.

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