A multi-phase motor overmodulation method based on segmented harmonic injection

Abstract

The present invention discloses a multi-phase motor overmodulation method based on segmented harmonic injection, which belongs to the field of high-performance drive technology for multi-phase motors for electric vehicles. According to different modulation ratios, for a multi-phase motor containing n harmonic planes, the entire overmodulation area is divided into n subspaces, and the boundaries are determined based on the constraint limit condition that the voltage vector distributed on the higher-order harmonic plane is zero. In the subspace with a relatively small modulation ratio, only low-order harmonics are injected; as the modulation ratio increases, the higher-order harmonic planes are activated in turn, and in the nth subspace, the modulation ratio approaches the limit value, and harmonics are injected into each harmonic plane. The injected harmonic voltage is sorted according to the amplitude of each phase voltage, and the zero-sequence voltage is taken into account to calculate the final injected harmonic, and the sorted voltage is reset to obtain the voltage modulation signal of each phase. The present invention reduces the current THD and stator winding loss by regulating the injected harmonics, and is simple to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of high-performance driving of multi-phase motors for electric vehicles, and in particular to a multi-phase motor overmodulation method based on segmented harmonic injection. Background Art

[0002] The increased number of phases and control freedom offered by multiphase motors make them a promising alternative to three-phase motors in some applications. Compared to traditional three-phase motors, multiphase motors feature several harmonic planes in addition to the fundamental plane they share. This allows for many unique uses of multiphase motors, such as fault diagnosis based on the relationship between harmonic and fundamental currents, current injection into the harmonic planes to ensure continuous, stable motor operation after a fault, and overmodulation by injecting voltage into the harmonic planes.

[0003] In new energy vehicles, motor operation must consider limitations due to the fixed battery voltage. Improving bus voltage utilization becomes a key consideration. Overmodulation technology can improve bus voltage utilization, making it a viable option for industrial applications. The harmonic plane of a multiphase motor does not contribute to torque generation, so harmonic voltages can be injected to increase the equivalent amplitude of the fundamental voltage, thereby improving bus voltage utilization. While the torque ripple caused by harmonic voltage injection is negligible, the resulting harmonic currents can cause additional copper losses. Developing an overmodulation algorithm that combines simplicity with reduced copper losses remains an unresolved challenge in overmodulation technology. Summary of the Invention

[0004] In response to the above-mentioned technical problems existing in the prior art, the present invention provides a multi-phase motor overmodulation method based on segmented harmonic injection. By rationally utilizing the degrees of freedom existing in the multi-harmonic plane and calculating the amplitude of the injected harmonic voltage in segments, the copper loss can be effectively reduced while taking into account simple implementation and a wide range of applications.

[0005] To achieve the above objectives, the present invention proposes a multi-phase motor overmodulation method based on segmented harmonic injection, comprising:

[0006] For a multi-phase motor with n harmonic planes, the overmodulation region is divided into n subspaces, and the boundaries of each overmodulation region are determined;

[0007] The current reference phase voltage modulation ratio is obtained according to the voltage amplitude, and the overmodulation region and the harmonic voltage and zero-sequence voltage to be injected are determined according to the modulation ratio.

[0008] Furthermore, the boundaries of each overmodulation region are determined based on the constraint limit condition that the high-order harmonic plane distribution voltage vector is zero.

[0009] Furthermore, the harmonic voltage to be injected satisfies the following conditions:

[0010] a. Does not affect the fundamental wave plane voltage vector;

[0011] b. The voltage vector of the high-order harmonic plane mapping is zero.

[0012] Furthermore, when calculating the harmonic voltage to be injected into the overmodulation region, the sorting modulation and restoration method is used to arrange the reference phase voltages in ascending order of amplitude and name them (v1,…,v i ,…,v 2n+1 ), n is the number of harmonic planes contained in the multiphase motor, v i Represents the phase voltage of the i-th position in the sorting; based on the sorted phase voltage, calculate the harmonic voltage v required to be injected into the phase corresponding to each sorting ji , that is, the harmonic voltage required to be injected into the phase at the ith position; after restoration, the harmonic voltage required to be injected into each reference phase is obtained.

[0013] Furthermore, the zero-sequence voltage calculation formula is:

[0014] v0=-0.5(v1+v j1 +v 2n+1 +v j(2n+1) )

[0015] Among them, v0 represents the zero sequence voltage, v1, v 2n+1 are the two phase voltages with the lowest and highest order, v j1 、v j(2n+1) These are the two desired injected harmonic voltages with the lowest and highest order respectively.

[0016] Furthermore, for a multiphase motor containing n harmonic planes, the overmodulation region is divided into n subspaces, and the overmodulation region corresponding to each subspace is recorded as The boundary of the overmodulation region is denoted as m k , k=1,2,…,n;

[0017] If the current reference voltage modulation ratio m is (m k-1 , m k ], the overmodulation area is When , m0 represents the boundary of the linear modulation area.

[0018] Furthermore, the modulation area is determined according to the current reference phase voltage modulation ratio After that, harmonic voltage and zero sequence voltage need to be injected into the determined modulation area, and different intervals (m k-1 , m k ]The corresponding harmonic voltages are different.

[0019] Furthermore, the harmonic voltage and the zero-sequence voltage are modulated into a given voltage signal through a triangular carrier, and the voltage signal is injected into each phase of the motor.

[0020] The beneficial technical effects of the present invention are as follows:

[0021] (1) The present invention proposes a multi-phase motor overmodulation method based on segmented harmonic injection. The overmodulation area of ​​a multi-phase motor with n harmonic spaces is divided into n overmodulation areas according to the modulation ratio, and the corresponding harmonics are reasonably injected. Different from the existing strategy, the harmonic reference voltage can reduce the current THD and copper loss.

[0022] (2) The present invention proposes a multi-phase motor overmodulation method based on segmented harmonic injection. The final modulation adopts a PWM carrier scheme, which optimizes the modulation process and takes zero-sequence voltage injection into consideration, making it easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a block diagram of the multi-phase motor overmodulation technology proposed in the present invention (taking a seven-phase motor as an example).

[0024] Figure 2 This is a fundamental wave plane voltage vector distribution diagram included in the present invention. DETAILED DESCRIPTION

[0025] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] For a multiphase motor containing n harmonic planes, the present invention divides the entire overmodulation region into n subspaces based on the modulation ratio. The boundaries of these subspaces are determined by satisfying the constraint that the voltage vector distributed on the higher-order harmonic planes is zero. In subspaces with smaller modulation ratios, only low-order harmonics and zero-sequence voltage are injected. As the modulation ratio increases, higher-order harmonic planes are activated sequentially. In the nth subspace, as the modulation ratio approaches the limit, harmonics and zero-sequence voltage are injected into all harmonic planes.

[0027] like Figure 1 The figure shows the block diagram of the seven-phase motor overmodulation technology proposed in the present invention. The drive system of the seven-phase induction motor consists of seven two-level voltage source inverters, a seven-phase induction motor and a controller. The bus voltage is V dc , the spatial distribution angle of each phase stator winding is θ=2π / 7.

[0028] The specific implementation process of the proposed overmodulation technology is as follows:

[0029] (1) Using the seven-phase vector space decoupling method, the phase voltage of the multi-phase motor is transformed by Clarke to obtain the voltage vectors in the corresponding three α-β planes.

[0030] First, convert the voltage switching quantity into phase voltage as follows:

[0031]

[0032] Among them, S a 、S b 、S c 、S d 、S e 、S f 、S g Represents the voltage switching value of each phase, v a 、v b 、v c 、v d 、v e 、v f 、v g Represents the voltage of each phase respectively.

[0033] Then the voltage vectors of the three α-β planes are constructed as follows:

[0034]

[0035] Among them, v α1 、v β1 、v α2 、v β2 、v α3 、v β3 They represent the voltage components of the voltage vectors in the three α-β planes along the α and β axes respectively, and v0 represents the zero-sequence voltage vector.

[0036] The fundamental wave plane voltage vector distribution diagram is as follows Figure 2 As shown in Figure 2, the third harmonic plane voltage vector distribution is similar to the fifth harmonic plane voltage vector distribution, and the voltage amplitude has been normalized according to the bus voltage. Figure 2 The number in is determined by the following formula:

[0037] n=64S a +32S b +16S c +8S d +4S e +2S f +S g

[0038] Where n represents the voltage vector number.

[0039] (2) For a seven-phase motor with two harmonic planes, the entire overmodulation region is divided into two subspaces. The current reference voltage modulation ratio is obtained based on the voltage amplitude. The rated modulation ratio is the ratio of the fundamental plane voltage amplitude to the bus voltage.

[0040] The voltage amplitude on the fundamental plane obtained in step (1) is 0.2857V dc , 0.5148V dc and 0.6420V dc The voltage vector is the research object, and its amplitude in the third harmonic plane is 0.2857V dc , 0.1272V dc and 0.2291V dc , the amplitudes at the fifth harmonic plane are 0.2857V dc , 0.3563V dc and 0.1586V dc , if the voltage of each harmonic plane is guaranteed to be 0, the following constraints can be obtained:

[0041]

[0042] The solution is:

[0043]

[0044] Then, the linear modulation region boundary can be determined as follows:

[0045]

[0046] Among them, m0 represents the boundary of the linear modulation area, and t1, t2, and t3 represent the duty cycles of the three voltage vectors.

[0047] When the modulation ratio continues to increase, voltage harmonics need to be injected into the third harmonic plane, and the voltage injection into the fifth harmonic plane remains at 0. At this time, only the voltage amplitude is 0.5148V dc and 0.6420V dc The voltage vector participates in the action, and its amplitude in the fifth harmonic plane is 0.3563V dc and 0.1586V dc , the constraints are as follows:

[0048]

[0049] The solution is:

[0050]

[0051] Therefore, the boundary of the first overmodulation region can be determined as follows:

[0052]

[0053] Wherein, m1 represents the boundary of the first overmodulation region.

[0054] Similarly, the second overmodulation region is only 0.6420V dc The voltage vector participates in the action, and the boundary of the second overmodulation region is determined as follows:

[0055]

[0056] Wherein, m2 represents the boundary of the second overmodulation area.

[0057] (3) Calculate the harmonic voltage based on segmented injection, as follows

[0058] When the phase voltage amplitude is as follows:

[0059] v e <v d <v f <v c <v g <v b <v a

[0060] The above voltages are named v1 to v7 in ascending order. The strategy proposed in this invention injects harmonic voltages without changing the fundamental plane. When the modulation ratio is between m0 and m1, it should not be mapped to the fifth harmonic plane. At this point, there is still an extra degree of freedom, and harmonic voltages only need to be injected into the third harmonic plane. The constraint of equal amplitudes of two sets of adjacent voltages should satisfy the following equation:

[0061]

[0062] Among them, v ji (i=1,2,3…,7) is the injected harmonic voltage. By solving the above equations, the expression for injected harmonics in the third harmonic plane is as follows:

[0063]

[0064] Similarly, when the modulation ratio is between m1 and m2, it is necessary to inject harmonic voltages into both harmonic planes. The above equations are modified to:

[0065]

[0066] By solving the above equations, the expression for injected harmonics is as follows:

[0067]

[0068] For a seven-phase motor, there are 14 possible relationships between the phase voltage amplitudes. For each of these relationships, the injected harmonic voltages are the same as above due to symmetry.

[0069] (4) In order to implement the proposed overmodulation strategy, the following steps need to be completed. The first step is the injection of zero-sequence voltage, which is calculated as follows:

[0070] v0=-0.5(v1+v j1 +v7+v j7 )

[0071] Each phase is injected with the same zero-sequence voltage. Secondly, because the above calculation depends on the relative magnitude of the voltages, it is first necessary to sort the current voltage amplitudes. After the calculation is completed, the phases need to be allocated according to the sorting, and the entire overmodulation technique can be completed through carrier modulation.

[0072] In a specific implementation of the present invention, a seven-phase motor overmodulation method based on segmented harmonic injection is:

[0073] Step 1: For a seven-phase motor containing two harmonic planes, divide the overmodulation region into two subspaces and determine the boundaries of each overmodulation region;

[0074] In this step, the calculation process of the two overmodulation region boundaries contained in the seven-phase motor refers to the above content and will not be repeated here. The final boundaries include: linear modulation region boundary m0 = 0.5129, first overmodulation region boundary m1 = 0.5877, and second overmodulation region boundary m2 = 0.6259.

[0075] Step 2: Calculate the current reference phase voltage modulation ratio according to the voltage amplitude, and determine the overmodulation region and the harmonic voltage and zero-sequence voltage to be injected according to the modulation ratio.

[0076] In this step, the overmodulation regions corresponding to the intervals where the reference phase voltage modulation ratios are located and the harmonic voltages to be injected refer to the above content. Specifically, if the current reference phase voltage modulation ratio m is between (m0, m1], the overmodulation region is the first overmodulation region, i.e., the third harmonic plane; the harmonic voltage and zero-sequence voltage to be injected in the third harmonic plane are:

[0077]

[0078] The current reference phase voltage modulation ratio m is between (m1, m2], then the overmodulation region is the second overmodulation region, namely the third harmonic plane and the fifth harmonic plane; the harmonic voltage and zero-sequence voltage that need to be injected into the two harmonic planes are:

[0079]

[0080] The harmonic voltage and zero-sequence voltage are modulated by a triangular carrier to give a given voltage signal, and the voltage signal is injected into each phase of the motor; before injection, the reference phase voltage is restored in ascending order of amplitude according to the above, and the harmonic voltage required to be injected into each reference phase can be obtained. The above description of the embodiment is to facilitate the understanding and application of the present invention by ordinary technicians in this field. The present invention is not limited to the above embodiment. Improvements and modifications made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the scope of protection of the present invention.

Claims

1. A multi-phase motor overmodulation method based on segmented harmonic injection, characterized in that: include: For a multi-phase motor with n harmonic planes, the overmodulation region is divided into n subspaces, and the boundaries of each overmodulation region are determined; The current reference phase voltage modulation ratio is obtained according to the voltage amplitude, and the overmodulation region and the harmonic voltage and zero-sequence voltage to be injected are determined according to the modulation ratio; When calculating the harmonic voltage to be injected into the overmodulation region, the sorting modulation and restoration method is used to arrange the reference phase voltages in ascending order of amplitude and name them (v1,…,v i ,…,v 2n+1 ), n is the number of harmonic planes contained in the multiphase motor, v i Represents the phase voltage of the i-th position in the sorting; based on the sorted phase voltage, calculate the harmonic voltage v required to be injected into the phase corresponding to each sorting ji , that is, the harmonic voltage required to be injected into the phase of the i-th order; after restoration, the harmonic voltage required to be injected into each reference phase is obtained; The zero-sequence voltage calculation formula is: v0=-0.5(v1+v j1 +v 2n+1 +v j(2n+1) ) Among them, v0 represents the zero sequence voltage, v1, v 2n+1 are the two phase voltages with the lowest and highest order, v j1 、v j(2n+1) are the two desired injected harmonic voltages with the lowest and highest order respectively.

2. A multi-phase motor overmodulation method based on segmented harmonic injection according to claim 1, characterized in that: The boundaries of each overmodulation region are determined based on the constraint limit condition that the high-order harmonic plane distribution voltage vector is zero.

3. The multi-phase motor overmodulation method based on segmented harmonic injection according to claim 1, characterized in that: The harmonic voltage to be injected satisfies the following conditions: a. Does not affect the fundamental wave plane voltage vector; b. The plane of harmonic voltage injection is determined based on the modulation ratio area.

4. The multi-phase motor overmodulation method based on segmented harmonic injection according to claim 1, characterized in that: For a multi-phase motor with n harmonic planes, the overmodulation region is divided into n subspaces, and the overmodulation region corresponding to each subspace is recorded as The boundary of the overmodulation region is denoted as m k , k=1,2,…,n; If the current reference voltage modulation ratio m is (m k-1 , m k ], the overmodulation area is When k=1, m0 represents the boundary of the linear modulation area.

5. The multi-phase motor overmodulation method based on segmented harmonic injection according to claim 4, characterized in that: Determine the modulation area based on the current reference phase voltage modulation ratio After that, harmonic voltage and zero sequence voltage need to be injected into the determined modulation area, and different intervals (m k-1 , m k ]The corresponding harmonic voltages are different.

6. The multi-phase motor overmodulation method based on segmented harmonic injection according to claim 1, characterized in that: The harmonic voltage and zero-sequence voltage are modulated into a given voltage signal through a triangular carrier, and the voltage signal is injected into each phase of the motor.

Images