Random Space Vector Pulse Width Modulation Method with Dual Random Switching Frequency Variation Range

Abstract

The present invention discloses a random space vector pulse width modulation method with a double random switching frequency variation range. The random modulation technology reasonably stipulates the primary variation range and the secondary variation range of the switching frequency. Each control cycle randomly selects random frequencies in the two variation ranges and adds them to obtain the switching frequency of the control cycle, thereby making the switching frequency more evenly distributed within a certain random variation range. The method disclosed by the present invention can make the high-order harmonics originally concentrated at the switching frequency and its multiples more evenly dispersed within the random switching frequency range while keeping the random variation range of the switching frequency unchanged, thereby obtaining a better harmonic dispersion effect than the traditional random switching frequency space vector pulse width modulation method, and improving the suppression effect of the random space vector pulse width modulation method on the electromagnetic interference of the inverter when the switching frequency variation range is narrow.

Description

Technical Field

[0001] The invention relates to the technical field of power generation, power transformation and power distribution, and in particular to a random space vector pulse width modulation method with a double random switching frequency variation range. Background Art

[0002] In recent years, with the rapid development of modern transportation tools such as electric vehicles, more electric aircraft, high-speed trains, and electric propulsion ships, electromagnetic compatibility has received more and more attention as one of the important evaluation indicators in the field of electrified transportation. When using traditional space vector pulse width modulation (SVPWM) technology, the output voltage generates a large number of high-order harmonics at the switching frequency and its integer multiples, which brings a lot of electromagnetic noise and interference, affecting the electromagnetic compatibility of the system.

[0003] Random SVPWM technology can achieve uniform dispersion of high-order harmonics originally concentrated at the switching frequency and its integer multiples into a wider range by randomizing the parameters of the switching function, thereby improving the electromagnetic compatibility of the system. Existing random SVPWM methods can be mainly divided into random switching frequency modulation method and random pulse position modulation method. Among them, the random switching frequency SVPWM method has a simple implementation principle and a relatively obvious harmonic dispersion effect.

[0004] Random switching frequencies are usually evenly distributed on both sides of the average switching frequency, and their maximum value is limited by the switching device. When the switching frequency variation range is wide, its minimum value is low, the output current ripple is large, and it may cause spectrum aliasing, causing the high-order harmonics between the switching frequency and its multiples to overlap each other, increasing electromagnetic interference. Therefore, in practical applications, the range of random switching frequency variation will be subject to certain restrictions. The harmonic dispersion effect of the random switching frequency SVPWM method is greatly affected by the size of the switching frequency variation range. When the switching frequency variation range is narrow, the harmonic dispersion effect of this method is weak.

[0005] To address this problem, the present invention proposes a random space vector pulse width modulation method with a dual random switching frequency variation range, which can achieve better harmonic dispersion effect and suppress electromagnetic interference when the switching frequency variation range is narrow. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies of the above-mentioned background technology and to provide a random space vector pulse width modulation method with a double random switching frequency variation range, thereby improving the traditional random switching frequency SVPWM method, performing two random changes on the switching frequency within a certain range, and improving the problem of large harmonic peak amplitude of the traditional random switching frequency modulation method when the switching frequency variation range is narrow.

[0007] The present invention adopts the following technical solutions to achieve the above-mentioned invention object:

[0008] A random space vector pulse width modulation method with a double random switching frequency variation range comprises the following steps:

[0009] Step (1), set the switching frequency variation range twice

[0010] Step (2), generating random frequencies respectively within the range of two switching frequency changes;

[0011] Step (3), calculating the switching frequency of the next control cycle based on the average switching frequency and the random frequencies generated twice;

[0012] Step (4), calculate the action time of each basic voltage vector according to the SVPWM algorithm and output a PWM signal.

[0013] Preferably, the random switching frequency variation range is Δf, the primary switching frequency variation range is Δf1, the secondary switching frequency variation range is Δf2, and the switching frequency variation range is the sum of the primary switching frequency variation range and the secondary average switching frequency variation range, that is, Δf=Δf1+Δf2.

[0014] Preferably, the specific method of step (2) is: generating two random numbers R1 and R2 in each control cycle, and generating two random frequencies Δf in the two switching frequency variation ranges. s1 and Δf s2 , where Δf s1 =R1·Δf1,Δf s2 =R2·Δf2.

[0015] The preferred specific method of step (3) is: calculating the switching frequency of the control cycle according to the two random frequencies generated in step (2), and the formula used is as follows:

[0016] f s =f s0 +Δf s1 +Δf s2 ,

[0017] Among them, f s is the switching frequency of the current control cycle, f s0 is the average switching frequency of the system, Δf s1 is the random frequency generated within the range of a switching frequency change, Δf s2 A random frequency is generated within the range of the secondary switching frequency variation.

[0018] The preferred specific method of step (4) is: according to the current control cycle switching frequency obtained in step (3), the action time of each basic voltage vector is calculated according to the SVPWM algorithm and a PWM signal is output.

[0019] Preferably, the two random numbers R1 and R2 are in the range of [-1, 1].

[0020] Compared with the prior art, the present invention adopts the above technical solution and has the following beneficial effects:

[0021] 1. The present invention provides a random space vector pulse width modulation method with a double random switching frequency variation range. By selecting a random frequency within two switching frequency variation ranges in each control cycle to randomize the switching frequency, the harmonic dispersion effect of the random SVPWM method can be improved when the switching frequency variation range is narrow, and electromagnetic interference can be further suppressed.

[0022] 2. The present invention provides a random space vector pulse width modulation method with a double random switching frequency variation range, which uses a software method to generate random numbers, does not increase hardware costs, and is easy to implement.

[0023] 3. The present invention provides a random space vector pulse width modulation method with a double random switching frequency variation range, which is a general technology suitable for three-phase and multi-phase motor drive systems and has strong applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A flow chart of a random space vector pulse width modulation method with a double random switching frequency variation range;

[0026] Figure 2 It is a schematic diagram of the three-phase inverter topology;

[0027] Figure 3 It is the basic voltage vector distribution diagram of three-phase inverter. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The random space vector pulse width modulation method with double random switching frequency variation range is as follows Figure 1 As shown, first, two switching frequency variation ranges are pre-set according to the system average switching frequency and the switching frequency variation range requirements. The switching frequency variation range is the sum of the primary switching frequency variation range and the secondary average switching frequency variation range. For example, the average switching frequency f s0 The switching frequency variation range is 10kHz, and the switching frequency variation range is required to be ±10%. The primary switching frequency variation range Δf1 is set to 750Hz, and the secondary switching frequency variation range Δf2 is set to 250Hz.

[0030] Then, two random numbers R1 and R2 are generated in the range of [-1, 1], and two random frequencies Δf are selected within the preset primary switching frequency variation range Δf1 and secondary switching frequency variation range Δf2. s1 and Δf s2 , where Δf s1 =R1·Δf1,Δf s2 =R2·Δf2. Then, the switching frequency of the control cycle is obtained by combining the calculation formula: f s =f s0 +Δf s1 +Δf s2 , where f s is the switching frequency of the current control cycle, f s0 is the average switching frequency of the system.

[0031] Finally, the PWM signal is generated based on the calculated switching frequency according to the SVPWM algorithm. Taking the three-phase inverter as an example, its topology is as follows Figure 2 As shown, the switch function is defined as S = [S a ,S b ,S c ], if S a =1, it means that the upper bridge arm of inverter phase a is turned on and the lower bridge arm is turned off; if S a =0, and vice versa. According to the different switch combinations of the six switch tubes, 8 voltage vectors can be obtained, and their distribution is as follows Figure 3 .

[0032] Determine the reference voltage vector U of the control cycle ref The sector where it is located and calculate the action time of the two adjacent basic vectors and the zero vector:

[0033]

[0034] Among them, T s is the switching period of the control cycle, that is, T s =1 / f s , T X and T Y They are the reference voltage vector U ref The action time of adjacent basic vectors in clockwise and counterclockwise directions, T0 and T7 are the action time of zero vectors U0 (000) and U7 (111) respectively. According to the above voltage vector action time calculation, the target voltage vector can be synthesized and the PWM signal can be output.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A random space vector pulse width modulation method with a double random switching frequency variation range, characterized in that: The following steps are involved: Step (1), setting two switching frequency variation ranges; the primary switching frequency variation range is Δf1, the secondary switching frequency variation range is Δf2, and the random switching frequency variation range Δf is the sum of the primary switching frequency variation range and the secondary average switching frequency variation range, that is, Δf=Δf1+Δf2; Step (2), generating random frequencies respectively within the range of two switching frequency changes; Step (3), calculating the current control cycle switching frequency based on the average switching frequency and the twice generated random frequencies; Step (4), calculating the action time of each basic voltage vector according to the SVPWM algorithm and outputting a PWM signal; The specific method of step (2) is: generating two random numbers R1 and R2 in each control cycle, and generating two random frequencies Δf in the two switching frequency variation ranges. s1 and Δf s2 , where Δf s1 =R1·Δf1,Δf s2 =R2·Δf2; The specific method of step (3) is: calculate the current control cycle switching frequency according to the two random frequencies generated in step (2), and the formula used is as follows: f s =f s0 +Δf s1 +Δf s2 , Among them, f s is the switching frequency of the current control cycle, f s0 is the average switching frequency of the system, Δf s1 is the random frequency generated within the range of a switching frequency change, Δf s2 A random frequency is generated within the range of the secondary switching frequency variation.

2. The random space vector pulse width modulation method with double random switching frequency variation range according to claim 1 is characterized in that: The specific method of step (4) is: according to the current control cycle switching frequency obtained in step (3), the action time of each basic voltage vector is calculated according to the SVPWM algorithm and a PWM signal is output.

3. The random space vector pulse width modulation method with double random switching frequency variation range according to claim 1 is characterized in that: The two random numbers R1 and R2 are in the range of [-1, 1].

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