A direct torque control method and system considering direct current bus voltage imbalance

Abstract

The application discloses a direct torque control method and system considering DC bus voltage imbalance, and relates to the field of motor control. The method comprises the following steps: determining the distribution law of voltage vectors in the fundamental wave alpha-beta subplane and the harmonic x-y subplane when the DC bus voltage is unbalanced; determining three groups of virtual vector groups according to the distribution law and a set condition; the set condition is that the distribution of three basic voltage vectors in the harmonic x-y subplane is greater than 180 degrees, and the three basic voltage vectors are composed of two large vectors and one medium vector in the fundamental wave alpha-beta subplane; obtaining the optimal virtual vector based on the three groups of virtual vector groups according to the DC bus voltage ratio, the sector K value, the system torque and the flux demand; sorting the switches in two two-level three-phase voltage source inverters according to the action time of the three basic vectors in a control period, obtaining the optimized switch sorting, and then controlling the voltage source inverters. The application can efficiently operate under the DC bus voltage imbalance.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and in particular to a direct torque control method and system that takes into account DC bus voltage imbalance. Background Technology

[0002] Dual three-phase permanent magnet synchronous motors are the most common type of multiphase motor, with their two sets of windings spatially offset by 30°. Compared to traditional three-phase permanent magnet synchronous motors, dual three-phase permanent magnet synchronous motors offer advantages such as high reliability, low torque ripple, high power, and lower DC bus voltage requirements. However, dual three-phase permanent magnet synchronous motors have different power supply topologies, such as parallel connection, series connection, and separate DC sources, as follows: Figures 2-4 As shown. Parallel-connected DC sources are the most widely studied topology, such as... Figure 2 As shown, in this topology, the DC bus voltages of the two three-phase voltage sources are balanced. However, two other topologies are more advantageous in certain applications. For example... Figure 3 As shown, a series-connected DC source topology can output twice the DC bus voltage (u). dc1 +u dc2 This is more advantageous for medium- and high-voltage wind power plants, such as... Figure 3 As shown. Because a higher DC bus voltage can save on boost inverters, reduce rated current and cable size, this can lower costs and system failure rates. However, in a series-connected DC source topology, differences between the two sets of motor windings or the two sets of three-phase voltage source inverters can lead to DC bus voltage imbalance. Separate DC source topologies, such as... Figure 4 As shown, it possesses high fault tolerance. When one DC source fails, the dual three-phase permanent magnet synchronous motor can operate as a three-phase permanent magnet synchronous motor; simultaneously, the separated DC source topology can integrate different energy sources. Therefore, the separated DC source topology has broad application prospects in hybrid electric vehicles and hybrid energy storage systems. Due to the different power supply methods of the two DC power sources, DC bus voltage imbalance can also occur. Existing literature utilizes the additional degrees of freedom of multiphase motors to address the DC bus voltage imbalance problem. However, current research on direct torque control considering DC bus voltage imbalance does not include any research on this issue. Summary of the Invention

[0003] The purpose of this invention is to provide a direct torque control method and system that takes into account DC bus voltage imbalance, and has a fast torque dynamic response capability.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] A direct torque control method considering DC bus voltage imbalance is disclosed. The power supply structure of the dual three-phase permanent magnet synchronous motor includes the dual three-phase permanent magnet synchronous motor, a first two-level three-phase voltage source inverter, a second two-level three-phase voltage source inverter, a first DC source, and a second DC source. The first DC source and the second DC source are either separate or connected in series. The direct torque control method considering DC bus voltage imbalance includes:

[0006] Based on the space vector decoupling technique, the distribution law of the voltage vector output by the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter when the DC bus voltage is unbalanced is obtained in the fundamental α-β subplane and the harmonic xy subplane.

[0007] The sector is determined based on the distribution pattern of the fundamental wave α-β subplane and the harmonic xy subplane;

[0008] Three sets of virtual vector groups are determined based on the distribution patterns of the fundamental α-β subplane and the harmonic xy subplane and the set conditions. The set conditions are that the distribution of the three basic voltage vectors in each virtual vector group in the harmonic xy subplane is greater than 180°, and the three basic voltage vectors are composed of two large vectors and one medium-large vector in the fundamental α-β subplane.

[0009] Based on three sets of virtual vector groups, the optimal virtual vector is determined according to the current DC bus voltage ratio, sector K value, current torque, desired torque, current flux linkage, and desired flux linkage; the sector K value is the sector position number; the DC bus voltage ratio is the ratio of the DC bus voltage of the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter.

[0010] Based on the fact that the amplitude of the virtual vector is zero in the harmonic xy subplane, the duration of action of the three basic vectors within the control period is calculated.

[0011] Based on the duration of action of the three basic vectors within the control cycle, and following the principle of central symmetry, the switches in the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter are sorted to obtain an optimized switch sorting.

[0012] The first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter are controlled according to the optimized switching sequence.

[0013] Optionally, when the DC bus voltages of the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter are unbalanced, the distribution law of the voltage vectors output in the fundamental α-β subplane and the harmonic xy subplane includes a group of vectors whose phases do not change with the ratio of the DC bus voltages.

[0014] Optionally, sectors are determined based on the distribution patterns of the fundamental α-β subplane and the harmonic xy subplane, specifically including: using vector groups whose phases do not change with the ratio of the DC bus voltage as the boundaries of the sectors.

[0015] Optionally, based on three sets of virtual vectors, the optimal virtual vector is determined according to the current DC bus voltage ratio, sector K value, current torque, desired torque, current flux linkage, and desired flux linkage, specifically including:

[0016] Select one virtual vector group from the three virtual vector groups based on the current DC bus voltage ratio;

[0017] Based on a selected virtual vector group, four candidate virtual vectors are determined according to the sector K value;

[0018] Based on four candidate virtual vectors, the optimal virtual vector is determined according to the current torque, the desired torque, the current flux linkage, and the desired flux linkage.

[0019] Optionally, the three sets of virtual vector groups are respectively the DC bus voltage ratios that satisfy and The virtual vector group at time, where k is the DC bus voltage ratio.

[0020] This invention discloses a direct torque control system considering DC bus voltage imbalance. The power supply structure of the dual three-phase permanent magnet synchronous motor includes the dual three-phase permanent magnet synchronous motor, a first two-level three-phase voltage source inverter, a second two-level three-phase voltage source inverter, a first DC source, and a second DC source. The first DC source and the second DC source are either separate or connected in series. The direct torque control system considering DC bus voltage imbalance includes:

[0021] The voltage vector distribution law determination module is used to obtain the distribution law of the voltage vector output by the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter in the fundamental α-β subplane and the harmonic xy subplane when the DC bus voltages are unbalanced, based on the space vector decoupling technology.

[0022] The sector determination module is used to determine the sector based on the distribution pattern of the fundamental α-β subplane and the harmonic xy subplane;

[0023] The virtual vector group determination module is used to determine three virtual vector groups based on the distribution patterns and set conditions of the fundamental wave α-β subplane and harmonic xy subplane.

[0024] The virtual vector determination module is used to determine the optimal virtual vector based on three sets of virtual vectors, according to the current DC bus voltage ratio, sector K value, current torque, desired torque, current flux linkage, and desired flux linkage; the sector K value is the sector position number; the DC bus voltage ratio is the ratio of the DC bus voltage of the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter;

[0025] The action time determination module is used to calculate the action time of the three basic vectors within the control period based on the fact that the amplitude of the virtual vector is zero in the harmonic xy subplane.

[0026] The switch sorting module is used to sort the switches in the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter according to the principle of central symmetry based on the action time of the three basic vectors within the control cycle, so as to obtain an optimized switch sorting.

[0027] The control module is used to control the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter according to the optimized switching sequence.

[0028] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0029] This invention determines three virtual vector groups based on the distribution patterns and setting conditions of the fundamental α-β subplane and the harmonic xy subplane. The setting conditions are that the distribution of the three basic voltage vectors in each virtual vector group in the harmonic xy subplane is greater than 180°, and the three basic voltage vectors are composed of two large vectors and one medium-large vector in the fundamental α-β subplane. The influence of DC link voltage imbalance is considered when selecting virtual vector groups, resulting in low current harmonics and balanced stator current in both winding groups. At the same time, the method proposed in this invention retains the simple structure of the classical direct torque control method, thus having a fast torque dynamic response capability. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 A schematic flowchart of a direct torque control method considering DC bus voltage imbalance is provided in an embodiment of the present invention.

[0032] Figure 2 A schematic diagram of a dual three-phase permanent magnet synchronous motor connected in parallel with a DC source;

[0033] Figure 3 A schematic diagram of a dual three-phase permanent magnet synchronous motor connected in series with a DC source;

[0034] Figure 4 Schematic diagram of a dual three-phase permanent magnet synchronous motor with DC source disconnection;

[0035] Figure 5 A schematic diagram illustrating the variation of vectors 36 and 37 on the fundamental α-β subplane and the change of DC bus voltage ratio k, provided in an embodiment of the present invention.

[0036] Figure 6 A schematic diagram illustrating the variation of DC bus voltage ratio k in the variation law of vectors 36 and 37 on the harmonic xy subplane provided in an embodiment of the present invention.

[0037] Figure 7 A schematic diagram illustrating the variation of vectors 4 and 39 on the fundamental α-β subplane and the change of DC bus voltage ratio k, provided in an embodiment of the present invention.

[0038] Figure 8 A schematic diagram illustrating the variation of vectors 4 and 39 on the harmonic xy subplane and the change of DC bus voltage ratio k, provided in an embodiment of the present invention.

[0039] Figure 9 A schematic diagram illustrating the variation of vectors 53 and 33 on the fundamental α-β subplane and the variation of the DC bus voltage ratio k, provided in an embodiment of the present invention.

[0040] Figure 10 This is a schematic diagram illustrating the variation of the DC bus voltage ratio k of vectors 53 and 44 on the harmonic xy subplane provided in an embodiment of the present invention.

[0041] Figure 11 A schematic diagram illustrating the variation of vectors 46 and 49 on the fundamental α-β subplane and the variation of the DC bus voltage ratio k, provided in an embodiment of the present invention.

[0042] Figure 12 A schematic diagram illustrating the variation of DC bus voltage ratio k in the variation law of vectors 46 and 49 on the harmonic xy subplane provided in an embodiment of the present invention.

[0043] Figure 13 A schematic diagram showing the distribution of voltage vectors in the fundamental α-β subplane and harmonic xy subplane under different DC bus voltage ratios k, provided in an embodiment of the present invention.

[0044] Figure 14 This is a schematic diagram of sector definition when k≤1 provided in an embodiment of the present invention;

[0045] Figure 15 This is a schematic diagram of sector definition when k>1 provided in an embodiment of the present invention;

[0046] Figure 16 This is a schematic diagram showing the distribution of the first virtual vector group provided in an embodiment of the present invention;

[0047] Figure 17 This is a schematic diagram showing the distribution of the second virtual vector group provided in an embodiment of the present invention;

[0048] Figure 18 This is a schematic diagram showing the distribution of the third virtual vector group provided in an embodiment of the present invention;

[0049] Figure 19 This is a schematic diagram of the optimal virtual vector determination process provided in an embodiment of the present invention;

[0050] Figure 20 A schematic diagram of an optimized switching sequence is provided for embodiments of the present invention;

[0051] Figure 21 This is a schematic diagram of a direct torque control system that considers DC bus voltage imbalance, provided as an embodiment of the present invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] The purpose of this invention is to provide a direct torque control method and system that takes into account DC bus voltage imbalance, and has a fast torque dynamic response capability.

[0054] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] This invention considers DC bus voltage imbalance and uses space vector decoupling technology to obtain the distribution law of voltage vector in the fundamental α-β subplane and harmonic xy subplane when DC bus voltage is unbalanced. The sector definition is simplified based on the voltage vector distribution law. Then, three sets of virtual vectors are proposed according to the change in the DC bus voltage ratio. Each virtual vector consists of two large vectors and one medium vector in the fundamental α-β subplane, and the amplitude of the virtual vector in the harmonic xy subplane is 0, suppressing current harmonics. The corresponding virtual vector set is selected according to the DC bus voltage ratio. The output virtual vector is selected based on the sector K, torque, and flux hysteresis output. The action time of each vector in the virtual vector is calculated. The switching sequence is optimized and input to the voltage source inverter.

[0056] Example 1

[0057] This embodiment provides a direct torque control method considering DC bus voltage imbalance, wherein the power supply structure of the dual three-phase permanent magnet synchronous motor includes the dual three-phase permanent magnet synchronous motor, a first two-level three-phase voltage source inverter, a second two-level three-phase voltage source inverter, a first DC source and a second DC source, wherein the first DC source and the second DC source are separate or connected in series.

[0058] Since the two DC sources are either separate or connected in series, there will be a DC bus voltage u of the first DC source. dc1 DC bus voltage u of the second DC source dc2 An unbalanced situation.

[0059] like Figure 1 As shown, the direct torque control method considering DC bus voltage imbalance includes the following steps:

[0060] Step 101: Based on the space vector decoupling technique, obtain the distribution law of the voltage vector output by the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter when the DC bus voltage is unbalanced in the fundamental α-β subplane and the harmonic xy subplane.

[0061] Based on space vector decoupling technology, the voltage transformation matrix of the power supply structure of the dual three-phase permanent magnet synchronous motor is expressed as:

[0062]

[0063] Among them, the middle u α u β u x u y u o1 and u o2These represent the voltages in the fundamental α-β subplane, the harmonic xy subplane, and the harmonic o1-o2 subplane, respectively. Since the neutral points of the two windings of the motor are isolated from each other, the voltages in the harmonic o1-o2 subplane can be ignored. A1 u B1 u C1 u A2 u B2 and u C2 Let A1, B1, C1, A2, B2, and C2 represent the phase voltages respectively, and their expressions are as follows:

[0064]

[0065]

[0066] Among them, u dc1 and u dc2 These represent the two DC bus voltages respectively. A six-phase two-level inverter (first two-level three-phase voltage source inverter and second two-level three-phase voltage source inverter) can output 2... 6 =64 basic voltage vectors (basic vectors), which can be derived from V i =S C2 S B2 S A2 S C1 S B1 S A1 The binary value definition of S, where S x (x = A1, B1, C1, A2, B2, C2) represents the on-state of the inverter, S x =1 indicates that the phase is on, otherwise it is off. V i It is the voltage vector formed by the i-th switching combination.

[0067] The large vectors include vector 36 and vector 37, with vector 36 represented as V. 36 Vector 37 is represented as V 37 Vectors 36 and 37 are symmetric vectors. For example, in the α-β and xy subplanes, the projected coordinates of vector 36 are respectively... and Figure 5 and Figure 6 The variation of symmetrical vectors 36 and 37 with the DC bus voltage ratio k is shown. Both the magnitude and phase of the larger vector change with the DC bus voltage ratio. The angle between vectors 36 and 37 in the α-β subspace changes from 30° to 60° as k→0, and from 30° to 0 as k→∞. k is the DC bus voltage ratio, which can be defined as:

[0068]

[0069] The vectors include vector 39 and vector 4. The coordinates of vector 39 in the α-β and xy subplanes are respectively... and The coordinates of vector 4 are respectively and from Figure 7 and Figure 8 It can be seen that even if the DC bus voltage ratio changes, the phase of the intermediate vector remains unchanged. When k changes from 1 to 0, the magnitude of vector 4 remains unchanged, while the magnitude of vector 39 becomes zero. When k changes from 1 to ∞, the magnitude of vector 39 remains unchanged, while the magnitude of vector 4 becomes zero.

[0070] Medium-sized vectors include vectors 53 and 44, while small vectors include vectors 46 and 49. The distribution patterns of these vectors can be obtained using the same principle; vectors 53 and 44 are as follows... Figure 9 and Figure 10 As shown, vectors 46 and 49 are as follows Figure 11 and Figure 12 As shown.

[0071] Thus, the voltage vector distributions of the fundamental α-β subplane and harmonic xy subplane when the DC bus voltage is unbalanced are obtained as follows: Figure 13 As shown.

[0072] The distribution patterns of the output voltage vectors in the fundamental α-β subplane and harmonic xy subplane of the first and second two-level three-phase voltage source inverters when the DC bus voltages are unbalanced include: the amplitude and phase of the voltage vectors in groups L1, L3, and L4 change with the ratio of the DC bus voltages. The amplitude of the voltage vector in group L2 changes with the ratio of the DC bus voltages, but the phase of the voltage vector in group L2 does not change with the ratio of the DC bus voltages.

[0073] Group L4 consists of large vector groups (vectors 36 and 37), group L3 consists of medium-large vector groups (vectors 53 and 44), group L2 consists of medium vector groups (vectors 39 and 4), and group L1 consists of small vector groups (vectors 46 and 49). Group L2 consists of vector groups whose phases do not change with the ratio of the DC bus voltage.

[0074] Step 102: Determine the sector based on the distribution patterns of the fundamental α-β subplane and the harmonic xy subplane.

[0075] Specifically, step 102 includes using the vector group L2, whose phase does not change with the ratio of the DC bus voltage, as the boundary of the sector.

[0076] When k≤1, the sector is as follows Figure 14 As shown, when k>1, the sector is as follows Figure 15As shown.

[0077] Step 103: Determine three sets of virtual vector groups based on the distribution patterns of the fundamental α-β subplane and the harmonic xy subplane and the set conditions; the set conditions are that the distribution of the three basic voltage vectors in each virtual vector group in the harmonic xy subplane is greater than 180°, and the three basic voltage vectors are composed of two large vectors and one medium-large vector in the fundamental α-β subplane.

[0078] The three sets of virtual vector groups satisfy the DC bus voltage ratio. and The virtual vector group at time, where k is the DC bus voltage ratio.

[0079] This invention uses virtual vectors to suppress current harmonics. 1) To ensure the amplitude of the virtual vector is zero in the harmonic xy subplane, three basic voltage vectors are required, and their distribution in the harmonic xy subplane is greater than 180°; 2) Simultaneously, to maximize the utilization rate of the DC bus voltage, the three basic voltage vectors consist of two large vectors and one medium-large vector in the fundamental α-β subplane. Based on these two requirements, the method proposed in this invention can... Applications. For example... Figure 16 As shown, the first virtual vector group (v vir_x+1 to v vir_x+12 Choose when k satisfies Virtual vector groups at time; such as Figure 17 As shown, the second virtual vector group (v vir_y+1 to v vir_y+12 Choose when k satisfies Virtual vector groups at time; such as Figure 18 As shown, the third virtual vector group (v vir_z+1 to v vir_z+12 Choose when k satisfies Virtual vector group at time.

[0080] Step 104: Based on the three sets of virtual vector groups, determine the optimal virtual vector according to the current DC bus voltage ratio, sector K value, current torque, desired torque, current flux linkage, and desired flux linkage; the sector K value is the sector position number; the DC bus voltage ratio is the ratio of the DC bus voltage of the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter.

[0081] Among them, such as Figure 19 As shown, step 104 specifically includes:

[0082] Based on the current DC bus voltage ratio k, a virtual vector group is selected from three virtual vector groups. Specifically, a virtual vector group corresponding to the range of k values ​​is selected from the first, second, and third virtual vector groups.

[0083] Based on a selected group of virtual vectors, four candidate virtual vectors are determined according to the sector K value. The value of K ranges from 1 to 12.

[0084] Based on four candidate virtual vectors, the optimal virtual vector is determined according to the current torque, the desired torque, the sum of the current flux linkage and the desired flux linkage, i.e., based on the torque T. e The changing trend and magnetic flux ψ s The changing trend determines the optimal virtual vector.

[0085] The four candidate virtual vectors are represented as v vir_j+(i+2) v vir_j+(i+5) v vir_j+(i+8) v vir_j+(i+11) , where j = x, y or z.

[0086] When the desired torque is greater than the current torque, the torque demand increases; when the desired torque is less than the current torque, the torque demand decreases. Similarly, when the desired flux linkage is greater than the current flux linkage, the flux linkage demand increases; when the desired flux linkage is less than the current flux linkage, the flux linkage demand decreases.

[0087] When both torque and flux requirements increase, the optimal virtual vector is v. vir_j+(i+2) .

[0088] When the torque demand decreases and the flux demand increases, the optimal virtual vector is v. vir_j+(i+11) .

[0089] When the torque demand increases and the flux linkage demand decreases, the optimal virtual vector is v. vir_j+(i+5) .

[0090] When both torque and flux requirements decrease, the optimal virtual vector is v. vir_j+(i+8) .

[0091] Step 105: Based on the fact that the amplitude of the virtual vector is zero in the harmonic xy subplane, calculate the duration of action of the three basic vectors within the control period.

[0092] Since the amplitude of the virtual vector in the harmonic xy subplane is 0, the duration of action of the three fundamental vectors satisfies the following formula:

[0093]

[0094] Among them, L i_x Lj_x , and L k_x These represent the magnitudes of the three fundamental vectors along the x-axis in the harmonic xy subplane; L i_y L j_y , and L k_y These represent the amplitudes of the three fundamental vectors along the y-axis in the harmonic xy subplane; T s T represents the control period. i T j , and T k The durations of action of the three basic vectors within the control cycle are represented as follows:

[0095]

[0096] Step 106: Based on the duration of action of the three basic vectors within the control cycle, and following the principle of central symmetry, sort the switches in the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter to obtain an optimized switch sorting.

[0097] Using three fundamental vectors as vector 36 (V) 36 ), Vector 37 (V 37 ), Vector 32 (V 32 For example, the designed switching sequence is as follows: Figure 20 As shown, the switching sequence is not only centrally symmetric, but also the number of switches per phase does not exceed 1, T 36 T represents the duration of action of vector 36. 37 T represents the duration of action of vector 37. 32 The vector 32 represents the duration of action. KA1 represents the A-phase switch of the first two-level three-phase voltage source inverter, KB1 represents the B-phase switch of the first two-level three-phase voltage source inverter, KC1 represents the C-phase switch of the first two-level three-phase voltage source inverter, KA2 represents the A-phase switch of the second two-level three-phase voltage source inverter, KB2 represents the B-phase switch of the second two-level three-phase voltage source inverter, and KC2 represents the C-phase switch of the second two-level three-phase voltage source inverter. A symmetrical switching sequence is beneficial for the implementation of digital controllers, and fewer switching operations can reduce system switching losses.

[0098] Step 107: Control the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter according to the optimized switching sequence.

[0099] Example 2

[0100] This embodiment provides a direct torque control system considering DC bus voltage imbalance, wherein the power supply structure of the dual three-phase permanent magnet synchronous motor includes the dual three-phase permanent magnet synchronous motor, a first two-level three-phase voltage source inverter, a second two-level three-phase voltage source inverter, a first DC source and a second DC source, wherein the first DC source and the second DC source are separate or connected in series.

[0101] like Figure 21 As shown, the direct torque control system considering DC bus voltage imbalance includes:

[0102] The voltage vector distribution law determination module 201 is used to obtain the distribution law of the voltage vector output by the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter in the fundamental α-β subplane and the harmonic xy subplane when the DC bus voltages are unbalanced, based on the space vector decoupling technology.

[0103] The sector determination module 202 is used to determine the sector based on the distribution pattern of the fundamental wave α-β subplane and the harmonic xy subplane.

[0104] The virtual vector group determination module 203 is used to determine three virtual vector groups based on the distribution patterns and set conditions of the fundamental wave α-β subplane and harmonic xy subplane.

[0105] The virtual vector determination module 204 is used to determine the optimal virtual vector based on three sets of virtual vectors, according to the current DC bus voltage ratio, sector K value, current torque, desired torque, current flux linkage, and desired flux linkage; the sector K value is the sector position number; the DC bus voltage ratio is the ratio of the DC bus voltage of the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter.

[0106] The action time determination module 205 is used to calculate the action time of the three basic vectors within the control period based on the fact that the amplitude of the virtual vector is zero in the harmonic xy subplane.

[0107] The switch sorting module 206 is used to sort the switches in the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter according to the action time of the three basic vectors in the control cycle and the principle of central symmetry, so as to obtain an optimized switch sorting.

[0108] The control module 207 is used to control the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter according to the optimized switching sequence.

[0109] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0110] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A direct torque control method considering DC bus voltage imbalance, wherein the power supply structure of a dual three-phase permanent magnet synchronous motor includes a dual three-phase permanent magnet synchronous motor, a first two-level three-phase voltage source inverter, a second two-level three-phase voltage source inverter, a first DC source and a second DC source, wherein the first DC source and the second DC source are separate or connected in series, characterized in that, The direct torque control method considering DC bus voltage imbalance includes: Based on the space vector decoupling technique, the distribution law of the voltage vector output by the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter when the DC bus voltage is unbalanced is obtained in the fundamental α-β subplane and the harmonic xy subplane. The sector is determined based on the distribution pattern of the fundamental wave α-β subplane and the harmonic xy subplane; Based on the distribution patterns of the fundamental α-β subplane and the harmonic xy subplane, and the set conditions, three sets of virtual vector groups are determined; the set conditions are that the distribution of the three basic voltage vectors in each virtual vector group in the harmonic xy subplane is greater than 180°, and the three basic voltage vectors are composed of two large vectors and one medium-large vector in the fundamental α-β subplane. Based on three sets of virtual vector groups, the optimal virtual vector is determined according to the current DC bus voltage ratio, sector K value, current torque, desired torque, current flux linkage, and desired flux linkage; the sector K value is the sector position number; the DC bus voltage ratio is the ratio of the DC bus voltage of the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter. Based on the fact that the amplitude of the virtual vector is zero in the harmonic xy subplane, the duration of action of the three basic vectors within the control period is calculated. Based on the duration of action of the three basic vectors within the control cycle, and following the principle of central symmetry, the switches in the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter are sorted to obtain an optimized switch sorting. The first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter are controlled according to the optimized switching sequence.

2. The direct torque control method considering DC bus voltage imbalance according to claim 1, characterized in that, The distribution law of the voltage vector output by the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter in the fundamental α-β subplane and the harmonic xy subplane when the DC bus voltage is unbalanced includes a group of vectors whose phase does not change with the ratio of the DC bus voltage.

3. The direct torque control method considering DC bus voltage imbalance according to claim 2, characterized in that, The sector is determined based on the distribution patterns of the fundamental α-β subplane and the harmonic xy subplane. Specifically, this includes using vector groups whose phases do not change with the ratio of the DC bus voltage as the boundaries of the sector.

4. The direct torque control method considering DC bus voltage imbalance according to claim 1, characterized in that, Based on three sets of virtual vectors, the optimal virtual vector is determined according to the current DC bus voltage ratio, sector K value, current torque, desired torque, current flux linkage, and desired flux linkage. Specifically, this includes: Select one virtual vector group from the three virtual vector groups based on the current DC bus voltage ratio; Based on a selected virtual vector group, four candidate virtual vectors are determined according to the sector K value; Based on four candidate virtual vectors, the optimal virtual vector is determined according to the current torque, the desired torque, the current flux linkage, and the desired flux linkage.

5. The direct torque control method considering DC bus voltage imbalance according to claim 1, characterized in that, The three sets of virtual vector groups satisfy the DC bus voltage ratio. and The virtual vector group at time, where k is the DC bus voltage ratio.

6. A direct torque control system considering DC bus voltage imbalance, wherein the power supply structure of a dual three-phase permanent magnet synchronous motor includes a dual three-phase permanent magnet synchronous motor, a first two-level three-phase voltage source inverter, a second two-level three-phase voltage source inverter, a first DC source and a second DC source, wherein the first DC source and the second DC source are separate or connected in series, characterized in that, The direct torque control system that considers DC bus voltage imbalance includes: The voltage vector distribution law determination module is used to obtain the distribution law of the voltage vector output by the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter in the fundamental α-β subplane and the harmonic xy subplane when the DC bus voltages are unbalanced, based on the space vector decoupling technology. The sector determination module is used to determine the sector based on the distribution pattern of the fundamental α-β subplane and the harmonic xy subplane; The virtual vector group determination module is used to determine three virtual vector groups based on the distribution patterns and set conditions of the fundamental wave α-β subplane and harmonic xy subplane. The virtual vector determination module is used to determine the optimal virtual vector based on three sets of virtual vectors, according to the current DC bus voltage ratio, sector K value, current torque, desired torque, current flux linkage, and desired flux linkage; the sector K value is the sector position number; the DC bus voltage ratio is the ratio of the DC bus voltage of the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter; The action time determination module is used to calculate the action time of the three basic vectors within the control period based on the fact that the amplitude of the virtual vector is zero in the harmonic xy subplane. The switch sorting module is used to sort the switches in the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter according to the principle of central symmetry based on the action time of the three basic vectors within the control cycle, so as to obtain an optimized switch sorting. The control module is used to control the first two-level three-phase voltage source inverter and the second two-level three-phase voltage source inverter according to the optimized switching sequence.

Images