Direct Torque Control Method for Dual Three-Phase Permanent Magnet Synchronous Motor Based on Duty Ratio Allocation

Abstract

The present invention discloses a direct torque control method for a dual three-phase permanent magnet synchronous motor based on duty ratio allocation. By using the method of space vector decoupling, the six phases of the dual three-phase permanent magnet synchronous motor are respectively mapped to three planes to generate four non-zero vectors with different amplitudes; two non-zero vectors are extracted from them and synthesized into two virtual vector sets; the main virtual vector and the slave virtual vector are obtained according to the evaluation parameters; the duty ratios of the main and slave virtual vectors are obtained by processing the evaluation parameters; by synthesizing the main virtual vector and the slave virtual vector into a voltage vector and applying it to the six-phase lines of the dual three-phase permanent magnet synchronous motor within one control period. The control method of the present invention solves the technical problems such as large current harmonic content, large torque and flux linkage fluctuations, and high hardware implementation difficulty of the dual three-phase permanent magnet synchronous motor, reduces the inherent 5th and 7th harmonic contents of the dual three-phase permanent magnet synchronous motor, reduces the torque and flux linkage fluctuations of the dual three-phase permanent magnet synchronous motor, and is convenient for hardware implementation.

Description

Technical Field

[0001] The present invention relates to a permanent magnet synchronous motor control method in the field of multiphase permanent magnet synchronous motor control, and proposes a direct torque control method based on a duty ratio distribution strategy for high-performance operation control of a dual three-phase permanent magnet synchronous motor. Background Technique

[0002] With the rapid development of power electronics technology, the successive emergence of advanced control theories and high-performance microprocessors has provided favorable conditions for implementing more complex motor control strategies. Scholars from various countries have also conducted more in-depth research on systems with low voltage and high power, and high reliability. Along with the substantial reduction in the manufacturing cost of permanent magnet materials, multiphase permanent magnet synchronous motors with numerous advantages have been widely used in daily life and industrial manufacturing. For important industries such as aerospace, electric vehicles, and ship drives with large power requirements and high reliability requirements, ordinary three-phase drive systems can no longer meet their needs, and a multiphase motor drive system with more obvious advantages needs to be used. Compared with ordinary three-phase motors, dual three-phase permanent magnet synchronous motors have many advantages such as small torque ripple, strong fault tolerance ability, and the ability to achieve low voltage and high power.

[0003] The development process of direct torque control is relatively long and the technology is relatively mature. Compared with other control strategies, direct torque control can reduce complex coordinate transformations and has a fast dynamic torque response ability. For the six-phase inverter that drives the operation of a dual three-phase permanent magnet synchronous motor, there will be numerous voltage vectors with different amplitudes and directions, which greatly increases the design difficulty of the direct torque control method for dual three-phase permanent magnet synchronous motors.

[0004] However, there are still many problems with the direct torque control method for dual three-phase permanent magnet synchronous motors: when its mathematical model generates three mutually perpendicular sub-planes, the leakage inductance in the harmonic sub-plane will cause the motor to generate large 5th and 7th current harmonics during operation; secondly, the control effects of electromagnetic torque and stator magnetic flux are inaccurate, and there are problems such as large torque and magnetic flux fluctuations; at the same time, the virtual vectors synthesized by different duty ratio values will generate asymmetric switching sequences, which greatly increases the hardware implementation difficulty and reduces the effectiveness of harmonic suppression. Summary of the Invention

[0005] In order to solve the technical problems such as large current harmonic content, large torque and magnetic flux fluctuations, and large hardware implementation difficulty of dual three-phase permanent magnet synchronous motors, the present invention proposes a direct torque control method based on duty ratio distribution for dual three-phase permanent magnet synchronous motors.

[0006] The technical solution of the present invention includes the following steps:

[0007] Step 1: For a dual three-phase permanent magnet synchronous motor, adopt the method of space vector decoupling. Map the six phases of the dual three-phase permanent magnet synchronous motor to three planes, namely the α-β sub-plane, the x-y sub-plane, and the o1-o2 sub-plane, to generate two non-zero vectors, synthesize two virtual vectors, and make the action effect of the virtual vectors in the x-y sub-plane zero.

[0008] In Step 1, specifically, map the six phases of the dual three-phase permanent magnet synchronous motor to the α-β sub-plane, the x-y sub-plane, and the o1-o2 sub-plane respectively, and the three sub-planes are perpendicular to each other in space. Among them, the components of the motor on the α-β sub-plane are fundamental wave components and participate in the electromechanical energy conversion. The x-y sub-plane and the o1-o2 sub-plane are harmonic sub-planes and do not participate in the electromechanical energy conversion. The neutral points of the two sets of windings of the dual three-phase permanent magnet synchronous motor are isolated from each other, and the o1-o2 sub-plane can be ignored. The remaining α-β sub-plane and x-y sub-plane will generate four non-zero vectors with different amplitudes. Then, extract two non-zero vectors from the four non-zero vectors to synthesize two virtual vector sets, and make the action effect of the synthesized virtual vector sets in the x-y sub-plane zero.

[0009] Step 2: Process to obtain the evaluation parameters of the selected virtual vector set according to the situation where the stator flux linkage is located in different sectors, and select the main virtual vector and the slave virtual vector according to the evaluation parameters.

[0010] Step 3: Process to obtain the duty cycles d m and d s of the main and slave virtual vectors;

[0011] Step 4: After normalizing the duty cycles d m and d s of the main and slave virtual vectors, obtain the actual duty cycles d′ m and d′ s . By synthesizing the main virtual vector and the slave virtual vector with their respective actual duty cycles d′ m and d′ s into a voltage vector, apply the voltage vector to the six-phase lines of the dual three-phase permanent magnet synchronous motor within the control period, so that the main and slave virtual vectors act together on the dual three-phase permanent magnet synchronous motor within one control period to achieve direct torque control.

[0012] When the main and slave virtual vectors act on the entire control period, the main and slave virtual vectors will form different switching sequences in different sectors. The number of switchings of the main and slave virtual vectors within one period is relatively large and the waveforms are asymmetric. According to the relationship between the average value of the output voltage and the pulse width and pulse position, the switching sequences of the main and slave virtual vectors can be re-corrected into symmetric waveforms, reducing the hardware implementation difficulty.

[0013] In the first step, four non-zero vectors are generated in the α-β sub-plane and the x-y sub-plane, namely 12 large non-zero vectors V Ln , 12 second-largest non-zero vectors V MLn , 24 medium non-zero vectors V Mn , and 12 small non-zero vectors V Sn , where n represents the ordinal number. The magnitudes of the four non-zero vectors are obtained by processing the following formula:

[0014]

[0015] In the formula, |V Ln |, |V MLn |, |V Mn |, and |V Sn | represent the magnitudes of the large non-zero vector, the second-largest non-zero vector, the medium non-zero vector, and the small non-zero vector respectively; U dc is the DC bus voltage.

[0016] In the first step, two non-zero vectors are extracted from the four non-zero vectors, and virtual vectors are synthesized by adjusting the action time of the two non-zero vectors, and two virtual vector sets are formed. There are two specific synthesis methods:

[0017] Two corresponding non-zero vectors are extracted from the four non-zero vectors, and by adjusting the action time of the two non-zero vectors, the action effect of the virtual vector in the x-y sub-plane is made zero, and two virtual vector sets are synthesized. The specific synthesis method is as follows: The first virtual vector set includes 12 virtual vectors, denoted by V 1n (n = 1,..., 12), and is synthesized using the large non-zero vector with magnitude |V Ln | and the second-largest non-zero vector with magnitude |V MLn |; The second virtual vector set includes 12 virtual vectors, denoted by V 2n (n = 1,..., 12), and is synthesized using the second-largest non-zero vector with magnitude |V MLn | and the small non-zero vector with magnitude |V Sn |.

[0018] Synthesis method of the first virtual vector set:

[0019]

[0020] Synthesis method of the second virtual vector set:

[0021]

[0022] In the formula, T sis the duration of a control period; t1, t2, and t3 are the action times of the large non-zero vector, the second-largest non-zero vector, and the small non-zero vector respectively; |V 1nαβ | and |V 1nxy | are the amplitudes of the first virtual vector in the α-β sub-plane and the x-y sub-plane respectively; |V 2nαβ | and |V 2nxy | are the amplitudes of the second virtual vector in the α-β sub-plane and the x-y sub-plane respectively.

[0023] According to the difference ΔT e in value between the torque reference value and the actual torque value, judge the operating state of the dual three-phase permanent magnet synchronous motor, and combine the difference ΔT e in the numerical range shown in the following formula between the torque reference value and the actual torque value, and select the set of virtual vectors to be applied to the motor:

[0024]

[0025] In the formula, ΔT e represents the difference between the torque reference value and the actual torque value, B T represents the hysteresis width of the torque hysteresis controller, Δψ s represents the difference between the flux reference value and the actual flux value, V′ n (n = 1, …, 12) is the set of virtual vectors selected under different operating states; B T represents the hysteresis width of the torque hysteresis controller.

[0026] In the second step, with the stator flux direction as the x ψ axis, and the axis leading the x ψ axis by 90° as the y ψ axis, establish the stator flux coordinate system x ψ -y ψ .

[0027] In the second step, the evaluation parameters of the set of virtual vectors V′ n are calculated according to the following formula:

[0028]

[0029] In the formula, λ T , λ ψ and λ e are the torque evaluation parameter, the flux evaluation parameter, and the back electromotive force evaluation parameter respectively; V yψ and V xψ are the components of the set of virtual vectors V′ n on the stator flux x ψ axis and y ψ axis respectively; |Vαβ | is the amplitude of the virtual vector synthesized in the α-β sub-plane. When the first set of virtual vectors is selected, the amplitude is |V 1nαβ |, and when the second set of virtual vectors is selected, the amplitude is |V 2nαβ |; ω is the angular frequency; ψ s is the amplitude of the stator flux linkage.

[0030] In the second step, according to the selected set of virtual vectors, each virtual vector is calculated 12 times to obtain 12 sets of evaluation parameters. The virtual vector with the largest torque evaluation parameter is selected as the main virtual vector, and the virtual vector with the largest flux linkage evaluation parameter is selected as the slave virtual vector. The main virtual vector and the slave virtual vector do not coincide and both satisfy the requirements of torque and flux linkage increase and decrease at the same time.

[0031] Combined with the first step, the dual three-phase permanent magnet synchronous motor selects different amplitude sets of virtual vectors under different operating states. In one cycle, the main and slave virtual vectors act together, and a voltage vector with an adjustable amplitude and direction can be synthesized and applied to the motor.

[0032] The torque and flux linkage evaluation parameters can more accurately represent the influence degree of the selected main and slave virtual vectors on the torque and flux linkage of the dual three-phase permanent magnet synchronous motor.

[0033] The above processing of the present invention is no longer limited to selecting voltage vectors in only 12 fixed directions in each control cycle, which expands the selection range of the voltage vectors of the dual three-phase permanent magnet synchronous motor.

[0034] The above processing of the present invention enables the dual three-phase permanent magnet synchronous motor to select different amplitude virtual vectors under different torque error conditions. In one cycle, the main and slave virtual vectors act together, and a voltage vector with an adjustable amplitude and direction can be synthesized and applied to the motor. At the same time, the torque evaluation parameter and the flux linkage evaluation parameter can more accurately represent the influence degree of the selected main and slave virtual vectors on the torque and flux linkage of the dual three-phase permanent magnet synchronous motor.

[0035] In the third step, specifically, the torque equation and the flux linkage equation in the whole cycle are established by the evaluation parameters and the duty ratios of the main and slave virtual vectors as follows:

[0036]

[0037]

[0038] In the formula, Δψ s represents the difference between the flux linkage given value and the actual value of the flux linkage; L T is the torque coefficient; L ψ is the flux linkage coefficient; λ Tm and λ ψmThe torque evaluation parameter and the flux linkage evaluation parameter of the main virtual vector respectively; λ Ts and λ ψs The torque evaluation parameter and the flux linkage evaluation parameter of the slave virtual vector respectively; d m and d s respectively represent the calculated duty cycle values of the main virtual vector and the slave virtual vector.

[0039] Simultaneously solve the above formulas to calculate the duty cycles d m and d s of the main and slave virtual vectors.

[0040] In the fourth step described above, the duty cycles d m and d s of the main and slave virtual vectors are normalized according to the following formula to obtain the actual duty cycles d′ m and d′ s of the main and slave virtual vectors respectively:

[0041]

[0042] Furthermore, after step four, according to the relationship between the average value of the output voltage and the pulse width and pulse position, the switching sequences of the main and slave virtual vectors can be re-corrected. The correction rule is that the high-level action time of each phase of the corrected switching sequence remains unchanged, and the corrected virtual vectors also remain unchanged, ensuring that the action effects of the main and slave virtual vectors in the α-β sub-plane and the x-y sub-plane remain unchanged. And analyze the action order of non-zero vectors under different duty cycle values, which can avoid the hardware implementation difficulty brought by asymmetric switching sequences.

[0043] The control method of the present invention selects virtual vector sets with different amplitudes during the steady state and transient state of the dual three-phase permanent magnet synchronous motor, reducing the inherent 5th and 7th harmonic contents of the dual three-phase permanent magnet synchronous motor. Select the main and slave virtual vectors to act together in a control period according to the evaluation parameters, and re-calculate and allocate the duty cycles of the main and slave virtual vectors in combination with the specific values of the evaluation parameters, reducing the torque ripple and flux linkage ripple of the dual three-phase permanent magnet synchronous motor. Re-correct the generated six-phase switching sequence into a symmetric waveform, which is convenient for hardware implementation, and summarize the action order of non-zero vectors corresponding to different duty cycle sizes in the odd and even sectors.

[0044] The beneficial effects of the present invention are as follows: The present invention uses two virtual vector sets of a dual-three-phase permanent magnet synchronous motor to suppress the voltage amplitude in the x-y plane to zero, effectively reducing the 5th and 7th harmonics and improving the torque control accuracy at the same time; uses the accurate numerical values of the evaluation parameters to calculate and allocate the duty ratios of the master and slave virtual vectors, reducing the torque ripple and flux linkage ripple, and increasing the adjustment range of the vectors; re-corrects the switching sequences of the master and slave virtual vectors, so that the high-level action time of each phase of the corrected switching sequence remains unchanged, and the corrected virtual vectors are not changed either, ensuring the effectiveness of harmonic suppression while reducing the hardware implementation difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is the schematic diagram of the embodiment of the direct torque control method of a dual-three permanent magnet synchronous motor based on the duty ratio allocation strategy;

[0046] FIG. 2(a) is the spatial distribution diagram of non-zero voltage vectors in the α-β sub-plane;

[0047] FIG. 2(b) is the spatial distribution diagram of non-zero voltage vectors in the x-y sub-plane;

[0048] Figure 3 is the schematic diagram of virtual vector synthesis;

[0049] Figure 4 is the spatial distribution diagram of virtual vectors of two synthesis methods;

[0050] Figure 5 is the virtual vector switching sequence diagram of the first synthesis method;

[0051] Figure 6 is the master-slave virtual vector switching sequence diagram;

[0052] Figure 7 is the master-slave virtual vector switching sequence correction diagram of Sector I;

[0053] Figure 8 is the master-slave virtual vector switching sequence correction diagram of Sector II. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] The following will make a detailed description of the direct torque control method of a dual-three permanent magnet synchronous motor based on the duty ratio allocation strategy of the present invention in conjunction with the embodiments and the drawings.

[0055] The schematic diagram of the method of the present invention is as shown in Figure 1 and the method includes the following steps:

[0056] Step 1: By means of the space vector decoupling method, the six phases of the dual three-phase permanent magnet synchronous motor are respectively mapped to the α-β sub-plane, the x-y sub-plane and the o1-o2 sub-plane. The three sub-planes are perpendicular to each other in space. Among them, the components of the motor on the α-β sub-plane are fundamental wave components and participate in the electromechanical energy conversion. The x-y sub-plane and the o1-o2 sub-plane are harmonic sub-planes and do not participate in the electromechanical energy conversion. Since the neutral points of the two sets of windings of the dual three-phase permanent magnet synchronous motor are isolated from each other, the o1-o2 sub-plane can be ignored. The remaining α-β sub-plane and x-y sub-plane will generate four non-zero vectors with different amplitudes, namely 12 large non-zero vectors V Ln , 12 sub-large non-zero vectors V MLn , 24 medium non-zero vectors V Mn , 12 small non-zero vectors V Sn , where n represents the ordinal number. The distribution of the non-zero vectors in the α-β sub-plane and the x-y sub-plane is shown in Figure 2. The amplitudes of the four non-zero vectors are obtained by processing the following formulas:

[0057]

[0058] In the formula, |V Ln |, |V MLn |, |V Mn | and |V Sn | respectively represent the amplitudes of the large non-zero vector, the sub-large non-zero vector, the medium non-zero vector and the small non-zero vector; U dc is the DC bus voltage.

[0059] As shown in the virtual vector synthesis schematic diagram in Figure 3 , the large non-zero vector, the sub-large non-zero vector and the small non-zero vector have the same direction in the α-β sub-plane, but have opposite directions in the x-y sub-plane. Two non-zero vectors are extracted from the four non-zero vectors, and the virtual vector is synthesized by adjusting the action time of the two non-zero vectors, so that the action effect of the virtual vector in the x-y sub-plane is zero, and two virtual vector sets are obtained by composition. The specific synthesis method is as follows: The first virtual vector set includes 12 virtual vectors, denoted by V 1n (n = 1,..., 12), and is synthesized by using the large non-zero vector with an amplitude of |V Ln | and the sub-large non-zero vector with an amplitude of |V MLn |; The second virtual vector set includes 12 virtual vectors, denoted by V 2n (n = 1,..., 12), and is synthesized by using the sub-large non-zero vector with an amplitude of |V MLn | and the small non-zero vector with an amplitude of |V Sn |.

[0060] Synthesis method of the first virtual vector set:

[0061]

[0062] The synthesis method of the second virtual vector set:

[0063]

[0064] In the formula, T s is the duration of a control period; t1, t2, and t3 are the action times of the large non-zero vector, the second largest non-zero vector, and the small non-zero vector respectively; |V 1nαβ | and |V 1nxy | are the amplitudes of the first virtual vector in the α-β sub-plane and the x-y sub-plane respectively; |V 2nαβ | and |V 2nxy | are the amplitudes of the second virtual vector in the α-β sub-plane and the x-y sub-plane respectively.

[0065] It can be calculated that the action times t1 and t2, t2 and t3 of the two groups of virtual vectors are 0.731T s and 0.269T s , 0.578T s and 0.422T s . The spatial distribution of the two virtual vectors is as shown in Figure 4 , where the amplitude of the virtual vector of the first synthesis method in the α-β sub-plane is 0.597U dc , which is very close to the amplitude of the large non-zero vector, and has a large torque and flux linkage variation; the amplitude of the virtual vector of the second synthesis method in the α-β sub-plane is 0.345U dc , which is about half of the amplitude of the large non-zero vector, and can further reduce torque ripple.

[0066] Step 2: The dashed part of the block diagram as shown in Figure 1 judges the operating state of the dual three-phase permanent magnet synchronous motor according to the magnitude of the difference ΔT e between the torque reference value and the actual torque value, and selects the virtual vector set to be applied to the motor in combination with the range of the difference ΔT e between the torque reference value and the actual torque value shown in the following formula:

[0067]

[0068] In the formula, ΔT e represents the difference between the torque reference value and the actual torque value, B T represents the hysteresis width of the torque hysteresis controller, Δψ s represents the difference between the flux linkage reference value and the actual flux linkage value, V′ n(n = 1, …, 12) is the set of virtual vectors selected under different operating states; B T represents the hysteresis width of the torque hysteresis controller.

[0069] Taking the stator flux direction as the x ψ axis, and the axis leading the x ψ axis by 90° as the y ψ axis, a stator flux coordinate system x ψ -y ψ is established. The evaluation parameters of the virtual vector set V′ n are calculated according to the following formula:

[0070]

[0071] In the formula, λ T , λ ψ and λ e are the torque evaluation parameter, the flux evaluation parameter, and the back electromotive force evaluation parameter respectively; V yψ and V xψ are the components of the virtual vector set V n ′ on the stator flux x ψ axis and y ψ axis respectively; |V αβ | is the amplitude of the synthesized virtual vector in the α-β subplane. When the first virtual vector set is selected, the amplitude is |V 1nαβ |, and when the second virtual vector set is selected, the amplitude is |V 2nαβ |; ω is the angular frequency; ψ s is the stator flux amplitude.

[0072] According to the selected virtual vector set, each virtual vector is calculated 12 times to obtain 12 groups of evaluation parameters. The virtual vector with the largest torque evaluation parameter is selected as the main virtual vector, and the virtual vector with the largest flux evaluation parameter is selected as the slave virtual vector. The main virtual vector and the slave virtual vector do not coincide and both satisfy the requirements of increasing and decreasing torque and flux at the same time. For example Figure 4 Taking the I-th sector as an example, when the stator flux is in the I-th sector, according to the influence effects of the evaluation parameters corresponding to all virtual vectors, during the transient operation of the motor, the three virtual vectors V 11 , V 12 and V 13 of the first synthesis method can all increase the torque and the flux at the same time. The virtual vector V 13 with the largest torque evaluation parameter is selected as the main virtual vector, and the virtual vector V 11 with the largest flux evaluation parameter is selected as the slave virtual vector. Similarly, during the steady-state operation of the motor, the virtual vector V 23 of the second synthesis method is selected as the main virtual vector, and the virtual vector V 21is a slave virtual vector.

[0073] Step 3: Let the duty ratio calculation values of the master and slave virtual vectors be d m and d s . From the evaluation parameters and the duty ratios of the master and slave virtual vectors, the torque equation for the entire period can be obtained as follows:

[0074]

[0075] where L T is the torque coefficient; λ Tm and λ Ts are the torque evaluation parameters of the master and slave virtual vectors respectively.

[0076] Similarly, the expression of the flux linkage equation can be obtained as:

[0077]

[0078] where L ψ is the flux linkage coefficient; Δψ s represents the difference between the given flux linkage value and the actual flux linkage value; λ ψm and λ ψs are the flux linkage evaluation parameters of the master and slave virtual vectors respectively. By solving the simultaneous equations, the duty ratios d m and d s of the master and slave virtual vectors can be calculated.

[0079] The torque and flux linkage of the dual three-phase permanent magnet synchronous motor fluctuate greatly, and the inaccuracies of the torque coefficient and flux linkage coefficient result in the calculated duty ratios of the master and slave virtual vectors not necessarily being between 0 and 1. By reassigning and setting the duty ratios of the master and slave virtual vectors, a standardized value is achieved. The actual duty ratios d′ m and d′ s of the master and slave virtual vectors are obtained according to the following formula:

[0080]

[0081] Step 4: When a single virtual vector acts on the entire control period, two non-zero vectors will form different switching sequences in different sectors. As Figure 5 shown for V 11 and V 12 in the first synthesis method, in the switching sequence of a single virtual vector, the B-phase of the virtual vector V 12 has more switching times and an asymmetric waveform within a period. Similarly, as Figure 6 shown for the master and slave virtual vector switching sequences in the first and second sectors, the master and slave virtual vectors also have the problems of more switching times and an asymmetric waveform within a period, which will increase the difficulty of hardware implementation and also reduce the effect of harmonic suppression.

[0082] To avoid the hardware implementation difficulty brought by the asymmetric switching sequence, according to the relationship between the average value of the output voltage and the pulse width and pulse position, the switching sequences of the master-slave virtual vectors can be re-corrected, and the action order of the non-zero vectors under different duty cycle values can be analyzed. The correction rule is summarized as follows: the high-level action time of each phase of the corrected switching sequence remains unchanged, and the corrected virtual vectors also remain unchanged, ensuring that the action effects of the master-slave virtual vectors in the α-β sub-plane and the x-y sub-plane remain unchanged.

[0083] Taking the master-slave virtual vectors V 11 and V 13 、V 12 and V 14 in the first synthesis method in the first and second sectors as an example, analyze their switching sequence correction methods.

[0084] Since the duty cycle of the master-slave virtual vector varies, there are many cases for the corrected switching sequence. Below, according to the principle that the main virtual vector is dominant, the switching sequence correction methods for the odd and even sectors are analyzed in detail.

[0085] When the stator flux linkage is in the first sector, as Figure 7 shown;

[0086] When 0 < d′ m < 0.27, the non-zero vectors V L1 and V ML1 are replaced by the non-zero vectors V M1 、V L2 and V M4 ;

[0087] When 0.27 < d′ m < 0.73, the non-zero vectors V ML1 and V ML3 are replaced by the non-zero vectors V M1 、V L2 and V M4 ;

[0088] When 0.73 < d′ m < 1, the non-zero vectors V L3 and V ML3 are replaced by the non-zero vectors V M1 、V L2 and V M4 ;

[0089] When the stator flux linkage is in the second sector, as Figure 8 shown;

[0090] When 0 < d′ mWhen d′ < 0.5, the non - zero vectors V L2 , V ML2 and V ML4 are replaced by the non - zero vectors V L3 , V ML3 and V M8 ;

[0091] When 0.5 < d′ m <0.73, the non - zero vectors V L4 , V ML4 and V ML2 are replaced by the non - zero vectors V L3 , V ML3 and V M1 ;

[0092] When 0.73 < d′ m < 1, the non - zero vectors V L4 , V ML4 and V ML2 are replaced by the non - zero vectors V L1 , V L3 and V M1 .

[0093] For each of the remaining even - odd sectors, within the above three value ranges of d′ m , the non - zero vectors can be equivalently replaced by other different non - zero vectors to correct the asymmetric waveform into a symmetric waveform. Similarly, under steady - state operating conditions, the master - slave virtual vector switching sequence of the second synthesis method can also be symmetrically corrected according to this rule.

[0094] The present invention uses two virtual vector sets of a dual - three - phase permanent - magnet synchronous motor, and introduces an evaluation parameter to calculate and allocate the duty ratios of the master - slave virtual vectors, reducing the current harmonic content while also improving the control accuracy of torque and magnetic flux, suppressing torque ripple and magnetic - flux ripple; correcting the switching sequence of the master - slave virtual vectors into a symmetric waveform, while reducing the hardware implementation difficulty and also ensuring the effectiveness of harmonic suppression.

Claims

1. A direct torque control method for a dual three-phase permanent magnet synchronous motor based on duty ratio allocation, characterized in that: Step 1: For a dual three-phase permanent magnet synchronous motor, a space vector decoupling method is adopted. The six phases of the dual three-phase permanent magnet synchronous motor are respectively mapped to three planes, namely the α-b sub-plane, the x-y sub-plane, and the o1-o2 sub-plane, to generate two non-zero vectors, and two virtual vectors are synthesized, and the effect of the virtual vectors in the x-y sub-plane is zero; Step 2: Process to obtain the evaluation parameters of the selected virtual vector set, and select the main virtual vector and the slave virtual vector according to the evaluation parameters; Step 3: Process according to the evaluation parameters to obtain the duty cycles d m and d s ; Step 4: For the duty cycles d m and d s After normalization, the actual duty cycles d′ m and d s ′ of the master and slave virtual vectors are obtained. By synthesizing the master virtual vector and the slave virtual vector into a voltage vector with their respective actual duty cycles d′ m and d s ′, and applying the voltage vector to the six-phase lines of the dual three-phase permanent magnet synchronous motor in the control period, the master and slave virtual vectors act together on the dual three-phase permanent magnet synchronous motor within one control period; In the first step, four non-zero vectors are generated in the α-b sub-plane and the x-y sub-plane, namely 12 large non-zero vectors V Ln , 12 sub-large non-zero vectors V MLn , 24 medium non-zero vectors V Mn , and 12 small non-zero vectors V Sn , where n represents the ordinal number. The magnitudes of the four non-zero vectors are obtained by processing the following formula: Where, |V Ln |, |V MLn |, |V Mn | and |V Sn | respectively represent the large non-zero vector amplitude, the second-largest non-zero vector amplitude, the medium non-zero vector amplitude, and the small non-zero vector amplitude; U dc is the DC bus voltage; In the said Step 1, two non-zero vectors are extracted from four non-zero vectors, and the virtual vectors are synthesized by adjusting the action time of the two non-zero vectors, and two virtual vector sets are formed. Specifically, there are two synthesis methods: The synthesis method of the first virtual vector set: The synthesis method of the second virtual vector set: Where, T s is the duration of a control period; t1, t2, and t3 are the action times of the large non-zero vector, the second largest non-zero vector, and the small non-zero vector respectively; |V 1nab | and |V 1nxy | are the amplitudes of the first virtual vector in the α-b sub-plane and the x-y sub-plane respectively; |V 2nab | and |V 2nxy | are the amplitudes of the second virtual vector in the α-b sub-plane and the x-y sub-plane respectively; According to the difference ΔT between the torque given value and the actual torque value e to determine the operating state of the dual three-phase permanent magnet synchronous motor based on the magnitude of the value, and in combination with the difference ΔT between the torque given value and the actual torque value shown in the following formula e select the set of virtual vectors to act on the motor within the numerical range: where, ΔT e represents the difference between the torque reference value and the actual torque value, and B T represents the hysteresis width of the torque hysteresis controller, and Δy s represents the difference between the flux reference value and the actual flux value, and V n ￠(n = 1, …, 12) is the set of virtual vectors selected under different operating states; and B T represents the hysteresis width of the torque hysteresis controller; In the second step, the evaluation parameter of the virtual vector set V n ￠ is calculated according to the following formula: where λ T , l y and λ e are the torque evaluation parameter, the flux linkage evaluation parameter, and the back electromotive force evaluation parameter respectively; V yy and V xy are the components of the virtual vector set V n ￠ on the stator flux linkage x y axis and the y y axis respectively; |V ab | is the amplitude of the synthesized virtual vector in the α - b sub - plane, which is |V 1nab | when the first virtual vector set is selected and |V 2nab | when the second virtual vector set is selected; w is the angular frequency; y s is the amplitude of the stator flux linkage; The said Step 3 is specifically that the torque equation and the flux linkage equation in the whole period are established by the evaluation parameters and the duty ratios of the main and slave virtual vectors respectively as: where, Δy s represents the difference between the given flux linkage value and the actual flux linkage value; L T is the torque coefficient; L y is the flux linkage coefficient; λ Tm and l ym are the torque evaluation parameter and the flux linkage evaluation parameter of the main virtual vector respectively; λ Ts and l ys are the torque evaluation parameter and the flux linkage evaluation parameter of the slave virtual vector respectively; d m and d s represent the calculated duty ratios of the main virtual vector and the slave virtual vector respectively; Calculate the duty cycles d m and d s ; In the fourth step, for the duty cycles d m and d s normalize them according to the following formula to obtain the actual duty cycles d′ m and d s ′:

2. The direct torque control method for a dual three-phase permanent magnet synchronous motor based on duty ratio allocation according to claim 1, characterized in that: In the said Step 2, according to the selected virtual vector set, each virtual vector is calculated 12 times to obtain 12 groups of evaluation parameters. The virtual vector with the largest torque evaluation parameter is selected as the main virtual vector, and the virtual vector with the largest flux linkage evaluation parameter is selected as the slave virtual vector.

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