Spread spectrum modulation method based on Logistic discrete mapping

Abstract

The invention discloses a spread spectrum modulation method based on Logistic discrete mapping, and belongs to the field of signal spread spectrum modulation. The problem that an existing random spectrum spreading mode is weak in electromagnetic interference peak reduction capacity, and generated interference spectrums are not uniform is solved. A chaotic signal is generated based on an improved Logistic discrete mapping mode, the chaotic signal is sampled at intervals in a preset time period, each sampling result is superposed with a period of a reference signal to form a plurality of changing periods, and the plurality of changing periods form a spread spectrum period; and integrating the integral signal through an integrator, multiplying the integral result by the spread spectrum period to generate a variable frequency PWM signal, and modulating the switching frequency of the switching tube by the variable frequency PWM signal. The invention is mainly used for suppressing electromagnetic interference of equipment.

Description

Technical Field

[0001] The invention belongs to the field of signal spread spectrum modulation. Background Art

[0002] The peak of conducted electromagnetic interference will appear at the switching frequency. Spread spectrum modulation disperses the switching frequency around the fixed frequency, and the spectrum energy of conducted interference is no longer concentrated at the fixed switching frequency, thus reducing interference. Depending on the modulation signal, the frequency of spread spectrum modulation can be written as

[0003] f=f1+Δf

[0004] Where f1 is a fixed switching frequency and Δf is a variable frequency. Depending on the type of Δf, spread spectrum modulation can be periodic modulation or random modulation. When Δf is a periodic signal, such as a sine wave or square wave, it is periodic modulation. When Δf is a random signal, it is random modulation. Often, the interference spectrum of random modulation is more average than that of periodic modulation.

[0005] Periodic spread spectrum uses a fixed spectrum pattern for signal transmission. This fixed spectrum pattern is easy to predict and identify, which increases the risk of electromagnetic interference being detected. The spectrum characteristics of periodic spread spectrum also make the appearance of electromagnetic interference spikes regular. This regular interference spike is difficult to effectively suppress through traditional filtering and suppression technology, thus affecting the performance of related equipment systems.

[0006] Compared with periodic spread spectrum, random spread spectrum is more random in the spread spectrum sequence, which further reduces the peak of electromagnetic interference. However, the spectrum distribution of random spread spectrum is usually uneven. Random spread spectrum can only further reduce some peaks. Therefore, there are still peaks in the spectrum that have not been reduced, resulting in the electromagnetic interference intensity in some frequency bands is still too high, while other frequency bands are relatively weak. This uneven spectrum distribution increases the complexity and uncertainty of electromagnetic interference.

[0007] Therefore, the existing random spread spectrum method has a weak ability to reduce electromagnetic interference peaks, making the interference spectrum it generates uneven. The above problems need to be solved urgently. Summary of the invention

[0008] The purpose of the present invention is to solve the problem that the existing random spread spectrum method has a weak ability to reduce electromagnetic interference peaks, resulting in uneven interference spectrum generated by it, and provides a spread spectrum modulation method based on Logistic discrete mapping.

[0009] A spread spectrum modulation method based on Logistic discrete mapping, the method comprising:

[0010] A chaotic signal is generated based on an improved Logistic discrete mapping method, and the chaotic signal is sampled at intervals within a preset time period, and each sampling result is superimposed with the period of a reference signal to form a plurality of changing periods, which constitute a spread spectrum period;

[0011] The integrated signal is integrated by an integrator, and the integrated result is multiplied by the spread spectrum period to generate a variable frequency PWM signal, which is used to modulate the switching frequency of the switch tube;

[0012] In the process of generating the variable frequency PWM signal, when the spread spectrum frequency corresponding to the spread spectrum period is equal to the integration result, the integrator state is reset.

[0013] Preferably, the expression of the improved Logistic discrete mapping is x n+1 =1-λx n 2 ;

[0014] x n+1 is the n+1th mapping state, x n is the nth mapping state, and λ is the improved Logistic parameter.

[0015] Preferably, 0<λ≤2.

[0016] Preferably, the mapping range of the improved Logistic discrete mapping is [-1, 1].

[0017] Preferably, the generated chaotic signal is implemented using a chaotic signal generator;

[0018] The chaotic signal generator includes resistors R1 to R6, a resistor R8, a sliding rheostat R9, an amplifier U2A, an amplifier U2B, capacitors C1 to C2, an inductor L1, a power source V1 and a power source V2;

[0019] One end of the resistor R8 is connected to one end of the capacitor C2 and one end of the sliding resistor R9, and serves as an output end of the chaotic signal generator;

[0020] The other end of the resistor R8 is connected to one end of the inductor L1;

[0021] The other end of the sliding rheostat R9 is connected to one end of the capacitor C1, one end of the resistor R4, the same-direction input end of the amplifier U2A, one end of the resistor R1 and the same-direction input end of the amplifier U2B, and then serves as another output end of the chaotic signal generator; the two output ends of the chaotic signal generator are used to output the chaotic signal;

[0022] The inverting input terminal of the amplifier U2A is connected to one end of the resistor R6 and one end of the resistor R5 at the same time, and the output terminal of the amplifier U2A is connected to the other end of the resistor R5 and the other end of the resistor R4 at the same time;

[0023] The positive power input terminal of amplifier U2A is connected to the positive power input terminal of amplifier U2B and the positive output terminal of power supply V1 at the same time.

[0024] The negative input terminal of the power supply of amplifier U2A is connected to the negative input terminal of the power supply of amplifier U2B and the positive output terminal of the power supply V2 at the same time.

[0025] The inverting input terminal of the amplifier U2B is connected to one end of the resistor R2 and one end of the resistor R3 at the same time;

[0026] The output end of the amplifier U2B is connected to the other end of the resistor R1 and the other end of the resistor R2 at the same time;

[0027] The other end of the inductor L1 is simultaneously connected to the other end of the capacitor C2, the other end of the capacitor C1, the other end of the resistor R6, the negative output end of the power supply V2, the other end of the resistor R3 and the negative output end of the power supply V1.

[0028] Preferably, the amplifier U2A and the amplifier U2B are both TL082CD models.

[0029] An improved spread spectrum modulation device based on Logistic discrete mapping includes a storage device, a processor, and a computer program stored in the storage device and executable on the processor. The processor executes the computer program to implement the spread spectrum modulation method based on Logistic discrete mapping.

[0030] A computer-readable storage device stores a computer program, and when the computer program is executed, the spread spectrum modulation method based on Logistic discrete mapping is implemented.

[0031] A computer program product comprises a computer program, which implements the spread spectrum modulation method based on Logistic discrete mapping when executed by a processor.

[0032] Advantages of the present invention:

[0033] The present invention provides a spread spectrum modulation method based on Logistic discrete mapping, which generates a chaotic signal based on an improved Logistic discrete mapping method, so that the chaotic signal and the variable frequency PWM frequency are more uniform. After the switching frequency of the switch tube is modulated by the variable frequency PWM signal, the interference spectrum of the modulated device is more uniform. The method is easy to control and implement, and the electromagnetic compatibility and reliability of the device system are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the spread spectrum modulation method based on Logistic discrete mapping described in the present invention;

[0035] Figure 2 is a schematic diagram of the circuit structure of a chaotic signal generator;

[0036] Figure 3 This is a traditional Logistic chaotic state diagram; Figure 4 This is a schematic diagram of the improved Logistic chaotic state;

[0037] Figure 5 yes Figure 2 The waveform diagram of the chaotic signal generated by the chaotic signal generator shown in the figure; wherein each grid on the vertical axis is 1V, and each grid on the horizontal axis is 1MHz;

[0038] Figure 6 It is the waveform diagram of variable frequency PWM signal;

[0039] Figure 7 This is the interference spectrum diagram under chaotic spread spectrum of the present invention. DETAILED DESCRIPTION

[0040] 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.

[0041] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0042] Specific implementation method 1. Combination Figure 1 This embodiment describes a spread spectrum modulation method based on Logistic discrete mapping described in this embodiment, the method comprising:

[0043] A chaotic signal is generated based on an improved Logistic discrete mapping method, and the chaotic signal is sampled at intervals within a preset time period, and each sampling result is superimposed with the period of a reference signal to form a plurality of changing periods, which constitute a spread spectrum period;

[0044] The integrated signal is integrated by an integrator, and the integrated result is multiplied by the spread spectrum period to generate a variable frequency PWM signal, which is used to modulate the switching frequency of the switch tube;

[0045] In the process of generating the variable frequency PWM signal, when the spread spectrum frequency corresponding to the spread spectrum period is equal to the integration result, the integrator state is reset.

[0046] In this preferred embodiment, a spread spectrum modulation method based on Logistic discrete mapping generates a chaotic signal based on an improved Logistic discrete mapping method, so that the chaotic signal and the variable frequency PWM frequency are more uniform. After the switching frequency of the switch tube is modulated by the variable frequency PWM signal, the interference spectrum of the modulated device is more uniform. Specifically, chaotic modulation can make the PWM frequency conversion more uniform, so there are fewer spectrum peaks and the spectrum is more uniform. This method is easy to control and implement, and improves the electromagnetic compatibility and reliability of the equipment system.

[0047] Chaotic modulation is developed from random modulation. Thanks to the randomness and convenience of chaotic sequences, the interference spectrum under modulation is lower and more continuous. Logistic mapping is a classic one-dimensional chaotic mapping that can generate complex dynamic behaviors through an iterative process, including chaotic states with wide spectrum characteristics. This is a typical discrete nonlinear mapping. The power electronic converter has a fixed PWM period because x in the discrete mapping is n With x n+1 The relationship between them also has a sampling period, which can directly make the PWM period, that is, the sampling period is naturally suitable for discrete mapping.

[0048] The general mathematical form of the traditional Logistic mapping is:

[0049] x n+1 =λx n (1-x n );

[0050] λ is called the Logistic parameter, 0<λ≤4.

[0051] For different λ, different chaotic states will be shown, that is, {x n The value of} varies with λ. For each λ, take the discrete mapping stable {x n} sequence, forming a Logistic chaotic state, such as Figure 3 shown.

[0052] Figure 3 As can be seen, the Logistic mapping is distributed between 0 and 1. As λ increases, the mapping sequence {x nThe value of} also changes, gradually entering a chaotic state, especially when it approaches 4, the chaotic state is more obvious. However, the range of Logistic mapping does not meet the requirements of random modulation for variable frequency Δf, and it only increases the fixed frequency f1 but does not reduce it. Therefore, it is necessary to improve the traditional Logistic discrete mapping, and an improved Logistic discrete mapping method is proposed, which is as follows:

[0053] The expression of the improved Logistic discrete mapping is x n+1 =1-λx n 2 , the mapping range is [-1,1];

[0054] x n+1 is the n+1th mapping state, x n is the nth mapping state, and λ is the improved Logistic parameter.

[0055] In this preferred implementation, the mathematical expression of the Logistic map is improved, and the mapping range is extended to [-1, 1]. The chaotic state of the improved Logistic discrete map is as follows: Figure 4 As shown in the figure, the value range of the improved Logistic parameter λ is [0,2]. It can be seen that with the increase of λ, the improved Logistic mapping enters a chaotic state. When it approaches 2, the mapping range expands from [0,1] before the improvement to [-1,1], which meets the requirements of random modulation.

[0056] The spread spectrum modulation method of the present invention relies on an improved Logistic discrete mapping, the mathematical model of the improved Logistic discrete mapping is simple to implement, the spatial parameters are unique, and the optimal parameters can be obtained by changing the lambda value.

[0057] Another variable frequency Δf={x n}*k, chaotic modulation within the switching frequency range [f1-k, f1+k] can be realized. As the switching frequency range increases, the number of frequency points increases. The more frequency points there are, the lower the electromagnetic interference is, and the more uniform the spectrum is.

[0058] See also Figure 2 ,Furthermore, the generated chaotic signal is implemented by using a chaotic signal generator;

[0059] The chaotic signal generator includes resistors R1 to R6, a resistor R8, a sliding rheostat R9, an amplifier U2A, an amplifier U2B, capacitors C1 to C2, an inductor L1, a power source V1 and a power source V2;

[0060] One end of the resistor R8 is connected to one end of the capacitor C2 and one end of the sliding resistor R9, and serves as an output end of the chaotic signal generator;

[0061] The other end of the resistor R8 is connected to one end of the inductor L1;

[0062] The other end of the sliding rheostat R9 is connected to one end of the capacitor C1, one end of the resistor R4, the same-direction input end of the amplifier U2A, one end of the resistor R1 and the same-direction input end of the amplifier U2B, and then serves as another output end of the chaotic signal generator; the two output ends of the chaotic signal generator are used to output the chaotic signal;

[0063] The inverting input terminal of the amplifier U2A is connected to one end of the resistor R6 and one end of the resistor R5 at the same time, and the output terminal of the amplifier U2A is connected to the other end of the resistor R5 and the other end of the resistor R4 at the same time;

[0064] The positive power input terminal of amplifier U2A is connected to the positive power input terminal of amplifier U2B and the positive output terminal of power supply V1 at the same time.

[0065] The negative input terminal of the power supply of amplifier U2A is connected to the negative input terminal of the power supply of amplifier U2B and the positive output terminal of the power supply V2 at the same time.

[0066] The inverting input terminal of the amplifier U2B is connected to one end of the resistor R2 and one end of the resistor R3 at the same time;

[0067] The output end of the amplifier U2B is connected to the other end of the resistor R1 and the other end of the resistor R2 at the same time;

[0068] The other end of the inductor L1 is simultaneously connected to the other end of the capacitor C2, the other end of the capacitor C1, the other end of the resistor R6, the negative output end of the power supply V2, the other end of the resistor R3 and the negative output end of the power supply V1.

[0069] In this preferred embodiment, a chaotic signal generator with a simple structure and easy implementation is provided, and Figure 2 The waveform diagram of the chaotic signal generated by the chaotic signal generator shown in FIG. Figure 5 As shown;

[0070] Furthermore, in the application, the amplifier U2A and the amplifier U2B are both TL082CD.

[0071] Specific implementation method 2: The improved spread spectrum modulation device based on Logistic discrete mapping described in this implementation method includes a storage device, a processor, and a computer program stored in the storage device and executable on the processor. The processor executes the computer program to implement the spread spectrum modulation method based on Logistic discrete mapping as described in specific implementation method 1.

[0072] Specific implementation method three: A computer-readable storage device described in this implementation method stores a computer program, and when the computer program is executed, the spread spectrum modulation method based on Logistic discrete mapping as described in specific implementation method one is implemented.

[0073] Specific implementation method 4: A computer program product described in this implementation method includes a computer program, and when the computer program is executed by a processor, the spread spectrum modulation method based on Logistic discrete mapping as described in specific implementation method 1 is implemented.

[0074] Verification test:

[0075] The effectiveness of the present invention is described in conjunction with the following drawings, as follows:

[0076] use Figure 5 The variable frequency PWM signal generated by the chaotic signal shown in the figure, the variable frequency PWM signal of part of the time is intercepted as shown in the figure Figure 6 As shown in the figure, the electromagnetic interference spectrum driven by the variable frequency PWM signal is as follows: Figure 7 As shown, it can be seen that the spectrum has no peaks and the spectrum is relatively uniform as a whole, which proves that the present invention has a strong ability to reduce electromagnetic interference peaks.

[0077] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A spread spectrum modulation method based on Logistic discrete mapping, characterized in that: The method includes: A chaotic signal is generated based on an improved Logistic discrete mapping method, and the chaotic signal is sampled at intervals within a preset time period, and each sampling result is superimposed with the period of a reference signal to form a plurality of changing periods, which constitute a spread spectrum period; The integrated signal is integrated by an integrator, and the integrated result is multiplied by the spread spectrum period to generate a variable frequency PWM signal, which is used to modulate the switching frequency of the switch tube; In the process of generating the variable frequency PWM signal, when the spread spectrum frequency corresponding to the spread spectrum period is equal to the integration result, the integrator state is reset.

2. The spread spectrum modulation method based on Logistic discrete mapping according to claim 1 is characterized in that: The expression of the improved Logistic discrete mapping is x n+1 =1-λx n 2 ; x n+1 is the n+1th mapping state, x n is the nth mapping state, and λ is the improved Logistic parameter.

3. The spread spectrum modulation method based on Logistic discrete mapping according to claim 2 is characterized in that: 0<λ≤2.

4. The spread spectrum modulation method based on Logistic discrete mapping according to claim 1 is characterized in that: The mapping range of the improved Logistic discrete mapping is [-1,1].

5. The spread spectrum modulation method based on Logistic discrete mapping according to claim 1, characterized in that: The generated chaotic signal is realized by using a chaotic signal generator; The chaotic signal generator includes resistors R1 to R6, a resistor R8, a sliding rheostat R9, an amplifier U2A, an amplifier U2B, capacitors C1 to C2, an inductor L1, a power source V1 and a power source V2; One end of the resistor R8 is connected to one end of the capacitor C2 and one end of the sliding resistor R9, and serves as an output end of the chaotic signal generator; The other end of the resistor R8 is connected to one end of the inductor L1; The other end of the sliding rheostat R9 is connected to one end of the capacitor C1, one end of the resistor R4, the same-direction input end of the amplifier U2A, one end of the resistor R1 and the same-direction input end of the amplifier U2B, and then serves as another output end of the chaotic signal generator; the two output ends of the chaotic signal generator are used to output the chaotic signal; The inverting input terminal of the amplifier U2A is connected to one end of the resistor R6 and one end of the resistor R5 at the same time, and the output terminal of the amplifier U2A is connected to the other end of the resistor R5 and the other end of the resistor R4 at the same time; The positive power input terminal of amplifier U2A is connected to the positive power input terminal of amplifier U2B and the positive output terminal of power supply V1 at the same time. The negative input terminal of the power supply of amplifier U2A is connected to the negative input terminal of the power supply of amplifier U2B and the positive output terminal of the power supply V2 at the same time. The inverting input terminal of the amplifier U2B is connected to one end of the resistor R2 and one end of the resistor R3 at the same time; The output end of the amplifier U2B is connected to the other end of the resistor R1 and the other end of the resistor R2 at the same time; The other end of the inductor L1 is simultaneously connected to the other end of the capacitor C2, the other end of the capacitor C1, the other end of the resistor R6, the negative output end of the power supply V2, the other end of the resistor R3 and the negative output end of the power supply V1.

6. The spread spectrum modulation method based on Logistic discrete mapping according to claim 4 is characterized in that: The amplifier U2A and the amplifier U2B are both TL082CD.

7. An improved spread spectrum modulation device based on Logistic discrete mapping, comprising a storage device, a processor, and a computer program stored in the storage device and executable on the processor, characterized in that: The processor executes a computer program to implement the spread spectrum modulation method based on Logistic discrete mapping as claimed in any one of claims 1 to 6.

8. A computer-readable storage device storing a computer program, characterized in that: When the computer program is executed, the spread spectrum modulation method based on Logistic discrete mapping as claimed in any one of claims 1 to 6 is implemented.

9. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the spread spectrum modulation method based on Logistic discrete mapping as claimed in claims 1 to 6 is implemented.

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