Electric vehicle power assembly system based on six-phase independent current source inverter and control method

Abstract

The invention discloses an electric vehicle power assembly system based on a six-phase independent current source inverter and a control method, and relates to the technical field of electric vehicle power assemblies, and the control method comprises the following steps: a modulation method: adopting a space vector modulation SVM technology based on vector space decomposition VSD, dividing a modulation index range into two regions for modulation, low-harmonic output current is realized in the region I, and the modulation range can be linearly changed; a harmonic component expansion modulation index is injected in the region II through an optimization algorithm; the common-mode voltage CMV reduction method comprises the following steps: firstly selecting a switching state, then determining an optimal switching mode, and finally calculating and analyzing the common-mode voltage CMV to ensure that the common-mode voltage CMV is kept at a low level in the whole modulation process, so that the common-mode voltage CMV is reduced. The optimized power assembly system, the extended modulation range, harmonic optimization and the efficient common-mode voltage reduction method are combined, the performance of the power assembly system of the electric vehicle is comprehensively improved, and the safety and stability of the whole power assembly system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electric vehicle powertrains, and particularly to an electric vehicle powertrain system and control method based on a six-phase independent current source inverter. Background Art

[0002] With the global emphasis on environmental protection, electric vehicles, as one of the important means to reduce carbon emissions, have attracted much attention in their development. However, electric vehicles face many challenges, such as energy storage limitations, high costs, the demand for rare earth metals, and the improvement of the reliability and efficiency of the power system. The multiphase drive technology has gradually emerged in the field of electric vehicles due to its unique advantages. The multiphase drive can distribute the power to more phases, reduce the power / current rating of each phase, reduce the dependence on parallel devices, and improve the system reliability. At the same time, the multiphase drive also has significant advantages in fault-tolerant operation, torque density improvement, and reduction of DC link current ripple.

[0003] The current source inverter (CSI) exhibits advantages such as long life, strong short-circuit fault capability, no problem with dv / dt, a motor-friendly output waveform, and voltage boosting ability in medium and high power applications. Combining the multiphase drive with CSI technology is expected to develop a more reliable and efficient powertrain system for electric vehicles. However, there are still many technical problems to be solved in applying the combination of the two to the electric vehicle powertrain, such as how to optimize the topology structure, improve the modulation efficiency, and reduce the common-mode voltage.

[0004] In the prior art, the common-mode voltage (CMV) is a harmful problem that exists when a pulse width modulation (PWM) inverter drives an AC motor. It may cause electromagnetic interference (EMI), an increase in the motor shaft voltage, and an increase in leakage current, which may damage the motor insulation and affect the safety and stability of the entire drive system. To solve this problem, many methods have been proposed in existing research, such as adding additional circuits or modifying the modulation scheme. However, these methods have certain limitations, such as increasing costs, reducing the DC link utilization rate, or causing deterioration of the harmonic performance. Therefore, an electric vehicle powertrain system and control method based on a six-phase independent current source inverter are needed to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide an electric vehicle powertrain system and control method based on a six-phase independent current source inverter to solve the problems existing in the prior art as mentioned in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] An electric vehicle powertrain control method based on a six-phase independent current source inverter includes the following steps:

[0008] Modulation method: The space vector modulation (SVM) technology based on vector space decomposition (VSD) is adopted. The modulation index range is divided into two regions for modulation. In region I, low harmonic output current is achieved and the modulation range can be linearly changed. In region II, harmonic components are injected through an optimization algorithm to expand the modulation index.

[0009] Common mode voltage (CMV) reduction method: First, the switching states are selected, then the optimal switching pattern is determined, and finally, the CMV is calculated and analyzed to ensure that the CMV remains at a low level throughout the modulation process.

[0010] Preferably, the specific steps of the modulation method are as follows:

[0011] In region I, by setting the x and y components of the reference current to zero, the vector space decomposition (VSD) transformation is used to select appropriate large and medium vector combinations, such as vectors in group I L and I M1 to achieve low harmonic output current, while ensuring that the modulation range can be linearly changed. Taking the six-phase reference current vector as an example, its expression is:

[0012]

[0013] where m is the modulation index, I dc is the DC link current, and θ is the electrical angle;

[0014] In region II, appropriate harmonic components are calculated and injected into the x and y subspaces through an optimization algorithm to generate higher fundamental components and achieve the expansion of the modulation index. The goal of the optimization algorithm is to minimize the injected harmonic content while satisfying the constraints of the inverter operating principle;

[0015] By establishing the objective function where k is the coefficient of the injected harmonic, and according to the constraint conditions, the fmincon function in MATLAB combined with the MultiStart option is used to solve the optimization problem to determine the optimal harmonic coefficient.

[0016] Preferably, the specific process of the switching state selection is as follows:

[0017] To achieve a higher modulation index, vectors in group I L are mainly selected. These vectors have a large amplitude in the aβ subspace, which helps to improve the utilization rate of the DC link current. At the same time, appropriate zero state vectors are selected to reduce the CMV; in each sector, the selection of vectors follows specific rules. For example, in sector I, the selected vector combination makes the sector located between two large vectors, and the selection of other vectors takes into account the relative position relationship with the sector to achieve a better modulation effect.

[0018] Preferably, the specific process of determining the optimal switching pattern is as follows:

[0019] To reduce switching losses, the optimal switching pattern for each sector is determined by calculating the Space Vector Distance Function (SVDF). The SVDF evaluates the number of switching transitions by calculating the difference between adjacent switching states, and the switching sequence that minimizes the SVDF is selected as the optimal pattern.

[0020] Preferably, the specific process of calculating and analyzing the Common Mode Voltage (CMV) is as follows:

[0021] The Common Mode Voltage (CMV) is defined as the average of the sum of the voltages between the DC buses of two three-phase CSIs and the load neutral point. By reasonably selecting the switching states, the peak value and Root Mean Square (RMS) value of the CMV can be reduced; when calculating the CMV, the influence of the load power factor is considered. According to the formula where v cm1 and v cm2 are the common mode voltage components of the two three-phase CSIs respectively, and they are related to the switching states and the load phase voltages;

[0022] By analyzing the CMV characteristics under different switching states offline, the combination of switching states that can effectively reduce the CMV under different load power factors is selected to ensure that the CMV remains at a low level throughout the modulation process;

[0023]

[0024] where is the voltage between the DC rail of each three-phase CSI and its load neutral point. The total CMV calculation in the 2N configuration can be described as the average of and to include their influence;

[0025]

[0026] Defining the voltage as a function of the switching state S j is a step in calculating the CMV; in CSI1, the voltage is equal to the voltage of the phase activated by the selected switching state:

[0027]

[0028] where S k represents the state of the semiconductor switch, k is a counter, which is equal to odd numbers {1, 3, 5} for the upper switch and even numbers for the lower switch is the output phase voltage of CSI1 with respect to the neutral point n1;

[0029] Through the switches that depend on CSI2, the voltage groups of CSI2 can be easily derived in the same way.

[0030]

[0031] By substituting all the voltages in (3) of (2) into (4), the CMV relationship based on the previously discussed S-CSI can be found:

[0032]

[0033] An electric vehicle powertrain system based on a six-phase independent current source inverter includes an independent current source inverter S-CSI and an asymmetric six-phase motor. The output end of the independent current source inverter S-CSI is electrically connected to the asymmetric six-phase motor. The independent current source inverter S-CSI is composed of two three-phase inverters CSI, and each three-phase inverter CSI is powered by an independent DC-DC converter.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] The present invention combines an optimized powertrain system, an extended modulation range, harmonic optimization, and an efficient common-mode voltage reduction method, comprehensively improving the performance of the electric vehicle powertrain system and enhancing the safety and stability of the entire powertrain system. Brief Description of the Drawings

[0036] Figure 1 It is a schematic diagram of the linear modulation region division of the present invention.

[0037] Figure 2 It is a selected vector diagram of the present invention's solution.

[0038] Figure 3 It is the best sequence diagram of the proposed solution switching states in Sector I of the present invention.

[0039] Figure 4 It is a structural diagram of the electric vehicle powertrain system based on a six-phase independent current source inverter of the present invention. Detailed Embodiments

[0040] To make the technical means, creative features, achieved purposes, and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0041] Please refer to Figures 1-4 , the present invention provides the following technical solutions:

[0042] A control method for an electric vehicle powertrain based on a six-phase independent current source inverter, comprising the following steps:

[0043] Modulation method: Adopt the space vector modulation (SVM) technology based on vector space decomposition (VSD). Divide the modulation index range into two regions for modulation. In region I, achieve low harmonic output current and be able to linearly change the modulation range. In region II, inject harmonic components through an optimization algorithm to expand the modulation index.

[0044] The specific steps of the modulation method are as follows: In region I, by setting the x and y components of the reference current to zero, use the vector space decomposition (VSD) transformation to select appropriate large and medium vector combinations, such as vectors in group I L and I M1 to achieve low harmonic output current, and at the same time ensure that the modulation range can be linearly changed. Taking the six-phase reference current vector as an example, its expression is:

[0045]

[0046] where m is the modulation index, I dc is the DC link current, and θ is the electrical angle;

[0047] In region II, calculate and inject appropriate harmonic components into the x and y subspaces through an optimization algorithm to generate higher fundamental components and achieve the expansion of the modulation index (up to about 1.08). The goal of the optimization algorithm is to minimize the injected harmonic content while satisfying the constraints of the inverter operating principle.

[0048] By establishing the objective function where k is the coefficient of the injected harmonic, and according to the constraint conditions (such as the dwell time must be greater than or equal to zero), use the fmincon function in MATLAB combined with the MultiStart option to solve the optimization problem and determine the optimal harmonic coefficient.

[0049] The modulation method proposed by the present invention effectively expands the modulation index range by about 8%. In region I, low harmonic output current is achieved. In region II, higher fundamental components are obtained at the cost of minimal harmonic increase, improving the torque production capacity of the motor. At the same time, the total harmonic distortion (THD) of voltage and current is maintained at a low level, enhancing the overall efficiency and performance of the system.

[0050] Common mode voltage (CMV) reduction method: First, select the switching state, then determine the optimal switching pattern, and finally calculate and analyze the common mode voltage (CMV) to ensure that the common mode voltage (CMV) remains at a low level throughout the modulation process.

[0051] Principle of SVM scheme: It is implemented based on the VSD method. In a six-phase S-CSI, the four reference components of the output current are controlled by selecting appropriate switching states. Five-segment discontinuous SVM modulation is adopted, and in each sampling period T S According to the position of the current reference in the aβ subspace, four active switching states and a zero switching state are selected to achieve ampere-second balance and control the current components in the x and y subspaces to zero, thereby reducing system losses.

[0052] The specific process of the switching state selection is as follows: To achieve a higher modulation index, vectors in Group I are mainly selected. These vectors have a larger amplitude in the aβ subspace, which helps to improve the utilization rate of the DC link current. At the same time, appropriate zero-state vectors are selected to reduce the common-mode voltage CMV. In each sector, the selection of vectors follows specific rules. For example, in Sector I, the selected vector combination is such that the sector is located between two large vectors, and the selection of other vectors takes into account the relative position relationship with the sector to achieve a better modulation effect. The specific vector selection can refer to L ... Figure 2

[0053] The specific process of determining the optimal switching pattern is as follows: To reduce switching losses, the optimal switching pattern for each sector is determined by calculating the Space Vector Distance Function (SVDF). The SVDF evaluates the number of switching transitions by calculating the differences between adjacent switching states, and the switching sequence that minimizes the SVDF is selected as the optimal pattern. For example, in Sector I, after calculating and comparing the SVDFs of different sequences, a switching sequence such as (15 - 9 - 1 - 55 - 61) is determined (refer to Figure 3 ), which has a relatively small number of switching transitions, thereby reducing switching losses and improving the efficiency of the inverter.

[0054] The specific process of the calculation and analysis of the common-mode voltage CMV is as follows: The common-mode voltage CMV is defined as the average value of the sum of the voltages between the DC buses of two three-phase CSIs and the load neutral point. By reasonably selecting the switching states, the peak value and the root mean square (RMS) value of the common-mode voltage CMV can be reduced. When calculating the common-mode voltage CMV, the influence of the load power factor is considered. According to the formula where v cm1 and v cm2 are the common-mode voltage components of the two three-phase CSIs respectively, which are related to the switching states and the load phase voltages.

[0055] By offline analyzing the characteristics of the common-mode voltage CMV under different switching states, a combination of switching states that can effectively reduce the common-mode voltage CMV under different load power factors is selected to ensure that the common-mode voltage CMV remains at a low level throughout the modulation process.

[0056]

[0057] where is the voltage between the DC rail and the load neutral point of each three-phase CSI. The total CMV calculation in the 2N configuration can be described as the average value of those in (2) and to include their effects;

[0058]

[0059] Defining the voltage as a function of the switch state S j is a step in calculating the CMV; in CSI1, the voltage is equal to the voltage of the phase activated by the selected switch state:

[0060]

[0061] where S k represents the state of the semiconductor switch, k is a counter, which is odd {1, 3, 5} for the upper switch and even for the lower switch is the output phase voltage of CSI1 with respect to the neutral point n1;

[0062] By relying on the switches of CSI2, the voltage set of CSI2 can be easily derived in the same way

[0063]

[0064] By substituting all the voltages in (3) of (2) into (4), the CMV relationship based on the previously discussed S-CSI can be found:

[0065]

[0066] By carefully selecting the switch states, the present invention can significantly reduce the common-mode voltage while achieving a higher modulation index. Compared with the traditional vector classification technique (VCT), the proposed scheme can reduce the peak-to-peak value of the common-mode voltage (CMV P；P ) by about 45% and the root-mean-square value (CMV RMS ) by about 44%, effectively reducing problems such as electromagnetic interference (EMI), motor shaft voltage, and leakage current, and improving the reliability and safety of the system.

[0067] The present invention also provides an electric vehicle powertrain system based on a six-phase independent current source inverter, which includes an independent current source inverter S-CSI and an asymmetric six-phase motor. The output end of the independent current source inverter S-CSI is electrically connected to the asymmetric six-phase motor. The independent current source inverter S-CSI is composed of two three-phase inverters CSI, and each three-phase inverter CSI is powered by an independent DC-DC converter. This system can make full use of semiconductor devices without increasing the battery voltage or the DC link current. Compared with other configurations, it has the same number and rating of semiconductors, reduces the need for additional components, and improves the reliability of the system and the simplicity of the manufacturing process.

[0068] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A control method for an electric vehicle powertrain based on a six-phase independent current source inverter, characterized in that It includes the following steps: Modulation method: Adopt the space vector modulation (SVM) technology based on vector space decomposition (VSD). Divide the modulation index range into two regions for modulation. In region I, achieve low harmonic output current and be able to linearly change the modulation range. In region II, inject harmonic components through an optimization algorithm to expand the modulation index. Common-mode voltage (CMV) reduction method: First, perform switch state selection, then determine the optimal switch pattern, and finally calculate and analyze the CMV to ensure that the CMV remains at a low level throughout the modulation process.

2. The control method of an electric vehicle powertrain based on a six-phase independent current source inverter according to claim 1, wherein The specific steps of the modulation method are as follows: In region I, by setting the x and y components of the reference current to zero, the vector space decomposition (VSD) transformation is used to select appropriate large and medium vector combinations, such as I L and I M1 vectors in the group to achieve a low harmonic output current, while ensuring that the modulation range can be linearly changed. Taking the six-phase reference current vector as an example, its expression is: where m is the modulation index, I dc is the DC link current, and θ is the electrical angle; In region II, calculate and inject appropriate harmonic components into the x and y subspaces through an optimization algorithm to generate higher fundamental components and achieve the expansion of the modulation index. The goal of the optimization algorithm is to minimize the injected harmonic content while satisfying the constraints of the inverter operating principle. By establishing the objective function where k is the coefficient of the injected harmonic, and according to the constraint conditions, the fmincon function in MATLAB is used in combination with the MultiStart option to solve the optimization problem and determine the optimal harmonic coefficient.

3. The control method for an electric vehicle powertrain based on a six-phase independent current source inverter according to claim 1, characterized in that, The specific process of the switch state selection is as follows: To achieve a higher modulation index, vectors in Group I are mainly selected. These vectors have a large amplitude in the αβ subspace, which helps to improve the utilization rate of the DC-link current. At the same time, appropriate zero-state vectors are selected to reduce the common-mode voltage (CMV). In each sector, the selection of vectors follows specific rules. For example, in Sector I, the selected vector combination is such that the sector is located between two large vectors, and the selection of other vectors takes into account the relative position relationship with the sector to achieve a better modulation effect. L ​ 4. The control method of an electric vehicle powertrain based on a six-phase independent current source inverter according to claim 1, wherein The specific process of determining the optimal switch pattern is as follows: To reduce switching losses, determine the optimal switch pattern for each sector by calculating the space vector distance function (SVDF). The SVDF evaluates the number of switch transitions by calculating the difference between adjacent switch states, and selects the switch sequence with the minimum SVDF as the optimal pattern.

5. The control method of an electric vehicle powertrain based on a six-phase independent current source inverter according to claim 1, characterized in that The specific process of the CMV calculation and analysis is as follows: The common-mode voltage CMV is defined as the average value of the sum of the voltages between the DC buses of two three-phase CSIs and the load neutral point. By reasonably selecting the switching states, the peak value and the root-mean-square RMS value of the common-mode voltage CMV can be reduced; when calculating the common-mode voltage CMV, the influence of the load power factor is considered, according to the formula where v cm1 and v cm2 are the common-mode voltage components of the two three-phase CSIs respectively, and they are related to the switching states and the load phase voltages; Through offline analysis of the CMV characteristics under different switch states, select the switch state combinations that can effectively reduce the CMV under different load power factors to ensure that the CMV remains at a low level throughout the modulation process. where is the voltage between the DC rail of each three-phase CSI and its load neutral point, and the total CMV calculation in the 2N configuration can be described as the average of (2) and to include their effects; Define voltage As a function of the switch state S j is a step in calculating CMV; in CSI1, the voltage equals the voltage of the phase activated by the selected switch state: where S k represents the state of the semiconductor switch, k is a counter, equal to odd numbers {1, 3, 5} for the upper switch and even numbers for the lower switch is the output phase voltage of CSI1 with respect to the neutral point n1; By relying on the CSI2-based switch, the voltage group of CSI2 can be easily derived in the same way. By substituting all the voltages in (3) of (2) into (4), the CMV relationship based on the previously discussed S-CSI can be found:

6. An electric vehicle powertrain system based on a six-phase independent current source inverter, characterized in that It includes an independent current source inverter (S-CSI) and an asymmetric six-phase motor. The output end of the independent current source inverter (S-CSI) is electrically connected to the asymmetric six-phase motor. The independent current source inverter (S-CSI) is composed of two three-phase inverters (CSI), and each three-phase inverter (CSI) is powered by an independent DC-DC converter.

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