A carrier phase-shifted modulation method of a cascaded H-bridge multi-level power amplifier

Abstract

The application relates to the technical field of power electronic power conversion and modulation, and discloses a carrier phase-shift modulation method of a cascaded H-bridge multi-level power amplifier, which comprises the following steps: a chaotic modulation sequence, that is, a chaotic carrier, is generated based on Logistic chaotic mapping; random disturbance is introduced to calculate the chaotic carrier frequency of each carrier cycle; based on the chaotic carrier frequency, a common phase accumulation and independent phase offset mode is adopted to generate independent phase sequences of the chaotic carriers corresponding to various cascaded units, and then symmetric triangular carriers of various paths meeting the requirements of a predetermined modulation strategy are generated; and the symmetric triangular carriers of various paths are modulated according to the predetermined modulation strategy to generate PWM control pulses of the switching devices of the corresponding cascaded H-bridge power units. The carrier phase-shift modulation method of the application can realize chaotic carrier frequency conversion while accurately controlling the constant phase difference of the unit carriers.

Description

Technical Field

[0001] This invention belongs to the technical field of power electronic power conversion and modulation, specifically relating to a carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier. Background Technology

[0002] Power amplifiers, as core components of energy conversion, are widely used in defense and civilian fields, such as underwater acoustic communication transmission systems, servo motor drives, magnetic levitation control, and power electronic equipment testing systems. Traditional linear power amplifiers operate in the linear amplification region. Although the output signal distortion is low, operating in the linear region leads to high losses, severe heat generation, and low overall efficiency. To meet the application requirements of high voltage, high power, and high efficiency, switching-mode digital power amplifiers have gradually become mainstream. Among them, the cascaded H-bridge multilevel topology is widely used in the field of high-power amplifiers due to its advantages such as a large number of output levels, high equivalent switching frequency, low dv / dt, and modularity for easy expansion. It avoids the complex problems of capacitor voltage balance control without the need for a common DC bus.

[0003] In the control strategies of cascaded H-bridge power amplifiers, carrier phase-shift modulation (CPS-PWM) is the most widely used technique. This technique increases the equivalent switching frequency of the output voltage by controlling the triangular carrier waves of each cascaded unit to be staggered in phase by a certain angle, thereby reducing the size of the output filter and improving the output waveform quality. However, traditional carrier phase-shift modulation usually uses a fixed frequency carrier signal. A fixed switching frequency results in high-amplitude discrete harmonic spikes centered on the switching frequency and its harmonics in the output voltage spectrum. These concentrated spectral energies not only generate severe electromagnetic interference, affecting the normal operation of surrounding precision electronic equipment, but also produce howling noise in applications such as sonar or motor drives, resulting in poor concealment and electromagnetic compatibility.

[0004] To suppress electromagnetic interference and smooth spectral spikes, introducing chaotic spread spectrum technology for frequency conversion modulation has become an effective solution. By allowing the carrier frequency to change randomly within a certain range according to a chaotic sequence, concentrated harmonic energy can be dispersed across a wider frequency band, thereby reducing peak interference. However, applying chaotic frequency conversion technology to carrier phase-shift modulation of cascaded H-bridges presents challenges. The harmonic cancellation characteristics of carrier phase-shift modulation are highly dependent on the strict constancy of the phase difference between each unit carrier. While the carrier frequency is constantly changing chaotically, using traditional analog circuits or conventional counters to generate carriers makes it extremely difficult to maintain a precise and constant phase difference between units in real time while the frequency is dynamically changing. Once the phase difference shifts or jitters, the frequency doubling effect of the cascaded H-bridge will fail, and the low-order harmonic content of the output voltage will increase significantly, leading to waveform distortion. Existing frequency conversion modulation methods often have complex algorithms, making it difficult to achieve chaotic frequency conversion at low cost in hardware while ensuring an absolutely constant phase difference. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier, which achieves chaotic carrier frequency conversion while precisely controlling the constant phase difference of each unit's carrier.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier includes the following steps: Step 1: Generate a chaotic modulation sequence based on the Logistic chaotic mapping, and introduce random perturbations to calculate the chaotic carrier frequency corresponding to each carrier period; Step 2: Based on the chaotic carrier frequency, the independent phase sequence of the chaotic carrier corresponding to each cascaded unit is generated by using the common phase accumulation and independent phase offset method, thereby generating each symmetrical triangular carrier that meets the requirements of the predetermined modulation strategy. Step 3: Modulate each symmetrical triangular carrier wave according to the predetermined modulation strategy to generate PWM control pulses for the corresponding cascaded H-bridge power unit switching devices.

[0007] Furthermore, in step two, firstly, based on the chaotic carrier frequency, a corresponding frequency control word is generated using the Direct Digital Synthesis (DDS) principle. Then, a common phase accumulator is constructed based on the frequency control word to generate a reference phase sequence shared by all cascaded units. Next, a fixed digital phase offset is constructed, and combined with the reference phase sequence, an independent phase sequence corresponding to the chaotic carrier of each cascaded unit is generated. Finally, through a phase folding algorithm, the sawtooth waves corresponding to the independent phase sequences of each cascaded unit are converted into symmetrical triangular carriers, resulting in multiple chaotic carriers with constant phase difference and synchronous chaotic frequency changes.

[0008] Furthermore, assuming the cascaded H-bridge multilevel power amplifier consists of N cascaded units, corresponding to 2N symmetrical triangular carrier waves, the independent phases of the k-th chaotic carrier wave are calculated using the following formula. This forms an independent phase sequence. in, This represents the reference phase within the i-th clock cycle. This represents the digital phase offset corresponding to the k-th chaotic carrier wave; The digital phase offset is calculated using the following formula. , Where k is the carrier index, k=0,1,...,2N 1; The bit width of the DDS phase accumulator and the full-scale range of the phase accumulator. Corresponding to a 360° phase.

[0009] Furthermore, the frequency control word is calculated using the following formula. : in, This indicates the bit width of the DDS phase accumulator. Indicates the system clock frequency. This represents the chaotic carrier frequency corresponding to the nth carrier period; Any two adjacent terms in the reference phase sequence satisfy the following difference equation: in, This represents the reference phase during the i-th clock cycle.

[0010] Furthermore, the predetermined modulation strategy is set to a unipolar frequency doubling CPS-PWM modulation method.

[0011] Furthermore, in step one, the formula for calculating the chaotic carrier frequency is as follows: In the formula, This represents the chaotic carrier frequency corresponding to the nth carrier period. Indicates the reference carrier frequency. Indicates the frequency offset. Indicates the depth of the spread spectrum random perturbation. This represents the chaotic state variables in the chaotic modulation sequence generated by the Logistic chaotic mapping.

[0012] Furthermore, in step one, the iterative formula for the Logistic chaotic mapping is as follows: In the formula, This represents the chaotic state variable in the nth iteration. This represents the bifurcation parameter of the Logistic chaotic mapping. Furthermore, the bifurcation parameters The value range is 3.57~4. Compared with the prior art, the beneficial effects of the present invention are: 1. This invention establishes a common phase accumulation and independent phase offset architecture based on DDS, which decouples frequency change and phase control in the frequency domain, ensuring that the phase difference between each cascaded unit carrier remains strictly constant during the random jump of carrier frequency. This guarantees the harmonic cancellation characteristics of the cascaded H-bridge carrier phase shift modulation, improves the output waveform quality, and solves the problem that traditional analog circuits or timer methods cannot maintain a fixed phase difference during frequency conversion.

[0013] 2. This method introduces Logistic chaotic mapping to spread spectrum perturb the carrier frequency, dispersing the discrete harmonic energy originally concentrated at multiples of the switching frequency to a wider frequency band, significantly reducing harmonic peak values, reducing electromagnetic interference and acoustic noise to surrounding equipment, and improving the electromagnetic compatibility of the power amplifier.

[0014] 3. This method strictly locks the phase difference of each unit carrier during the chaotic frequency conversion process, ensuring that the equivalent switching frequency of the cascaded H-bridge is always 2N times the unit switching frequency, effectively suppressing the generation of low-order harmonics and guaranteeing high-quality output waveforms. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 (a) is the bifurcation diagram of the Logistic mapping of the present invention; Figure 2 (b) is the Lyapunov exponent plot of the Logistic mapping of the present invention; Figure 3 This is a schematic diagram of the six-channel chaotic carrier generation principle of the present invention; Figure 4 This is a circuit diagram of the three-unit cascaded H-bridge power amplifier of the present invention; Figure 5 This is a schematic diagram of the unipolar frequency doubling CPS-PWM modulation principle corresponding to the three-unit cascaded H-bridge power amplifier of the present invention; Figure 6This is a schematic diagram of the unipolar frequency doubling CPS-PWM modulation principle corresponding to the single-unit cascaded H-bridge power amplifier of the present invention. Detailed Implementation

[0016] To make the technical means, creative features, objectives and effects of the present invention easier to understand, the following embodiments, in conjunction with the accompanying drawings, specifically illustrate the carrier phase-shift modulation method of the cascaded H-bridge multilevel power amplifier of the present invention. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention.

[0017] This invention focuses on a three-unit cascaded H-bridge power amplifier. This topology consists of three identical H-bridge sub-modules connected in series, such as... Figure 4 As shown, each H-bridge unit is powered by an independent DC power supply and can output three voltage levels: +Vdc, 0, and -Vdc. Cascading three units can output a 7-level voltage waveform. The modulation method uses unipolar frequency-doubled carrier phase-shift modulation, requiring the generation of 6 triangular carriers. The phase difference between adjacent carriers is fixed at 60°, and the equivalent switching frequency is 6 times the carrier frequency.

[0018] The chaotic carrier phase-shift modulation method for the cascaded H-bridge multilevel power amplifier described in this embodiment is implemented as follows: Figure 1 As shown, the specific implementation steps are as follows: S1. First, the Logistic mapping is selected as the chaotic sequence generator to generate a chaotic modulation sequence.

[0019] The Logistic mapping is the most classic one-dimensional chaotic model, and its iterative formula is: In the formula, Let be the chaotic state variable in the nth iteration. Let be the bifurcation parameter of the Logistic map. To determine its chaotic interval, we need to calculate its Lyapunov exponent. For example... Figure 2 As shown, where Figure 2 (a) is the bifurcation graph of the Logistic mapping. Figure 2 (b) shows the Lyapunov exponent plot of the Logistic map. When the bifurcation parameter μ is between 3.57 and 4, the Lyapunov exponent is greater than 0, and the system is in a chaotic state. In this embodiment, the bifurcation parameter μ... Set the value to 4 for the initial iteration. To avoid falling into a fixed point or a short-period orbit, the system state variable is set to 0.321. It is fully distributed in the interval [0,1], exhibiting complete traversal.

[0020] S2. Based on the generated chaotic modulation sequence and reference carrier frequency, random perturbation is introduced to calculate the chaotic carrier frequency, i.e., the dynamic switching frequency, for each carrier cycle of the chaotic carrier.

[0021] To ensure that the frequency disturbance can revolve around the reference carrier frequency Symmetrical changes require the chaotic state variables to be... A linear mapping to the interval [-1, 1] uses the following linear transformation relationship: Then the chaotic carrier frequency corresponding to the nth carrier period is: Among them, chaotic carrier frequency In Random jumps within the interval cause frequency shift. , For the spread spectrum random perturbation depth, the frequency variation range can be expressed as: Thus, by adjusting The size of the reference carrier frequency can be flexibly controlled to adjust the degree of spectrum spread, thereby achieving a balance between harmonic suppression and system stability. In this embodiment, the reference carrier frequency... Take 50kHz, spread spectrum random perturbation depth Taking 20%, then the frequency offset 0.2 × 50 kHz = 10 kHz, and the dynamic switching frequency varies from 40 kHz to 60 kHz.

[0022] Step 3: Using the common phase accumulation and independent phase offset method, a fixed digital phase offset is superimposed on the reference phase sequence to generate the independent phase sequence corresponding to each stage unit, thereby generating a symmetrical triangular carrier, i.e. a chaotic carrier, that satisfies the unipolar frequency doubling CPS-SPWM strategy.

[0023] For the three-unit cascaded H-bridge power amplifier in this system, a unipolar frequency-doubling CPS-SPWM strategy is adopted. This strategy requires the system to generate six triangular carriers with a fixed phase difference of 60° between adjacent carriers. At a fixed frequency, the fixed phase difference corresponds to a fixed time delay; however, during chaotic modulation, the carrier period... If a fixed time delay method is still used, the carrier phase of each unit will be disordered as the frequency changes randomly with each cycle, thus destroying the multi-level superimposed waveform.

[0024] To maintain a constant phase difference between variable-frequency carriers, this invention establishes a parallel synchronization mechanism based on the discrete phase domain, using direct digital frequency synthesis (DDS) theory. It employs a common phase accumulation and independent phase offset method, superimposing a fixed digital phase offset onto the reference phase sequence to generate independent phase sequences corresponding to each stage of the cascaded unit. This, in turn, generates a symmetrical triangular carrier that satisfies the unipolar frequency doubling CPS-SPWM strategy. Figure 3 The schematic diagram shows the generation of six symmetrical triangular carriers in CPS-PWM after introducing chaotic random perturbation.

[0025] First, based on the chaotic carrier frequency, the corresponding frequency control word is generated using the Direct Digital Frequency Synthesis (DDS) principle. It is related to the chaotic carrier random frequency. and system clock The correspondence is determined by the sampling theorem and the accumulator bit width M, and its calculation formula is: In this embodiment, the bit width of the DDS phase accumulator used based on the Direct Digital Frequency Synthesis (DDS) principle is... Take 32 bits, system clock frequency Using 100MHz as an example, the frequency control word is changed using this formula. This allows for precise control of the output carrier frequency in each clock cycle, while maintaining the continuous accumulation characteristic of phase changes, providing a theoretical basis for chaotic frequency conversion.

[0026] Then, a common phase accumulator is constructed based on the frequency control word to generate a reference phase sequence shared by all cascaded units. Any two terms in this reference phase sequence satisfy the following difference equation: In the formula, Let i be the reference phase for the i-th clock cycle, and the initial conditions be... [0] is a free variable and can take the value 0. 2 M-1 Any value between [a certain value]. All cascaded units share the same dynamically changing frequency control word. This ensures that the reference phase of all units is completely synchronized at any given time, fundamentally avoiding the phase asynchrony problem caused by frequency changes. Under this mechanism, all cascaded units share the same dynamically changing phase increment sequence, i.e., the frequency control word K[n], which means that the reference phase sequence of all cascaded units is the same. It is fully synchronized.

[0027] Subsequently, for the k-th chaotic carrier (k=0,1,...,5), a fixed digital phase offset is constructed as follows: DDS phase accumulator full scale Corresponding to a 360° phase, the phase offset between two adjacent chaotic carriers is fixed at 1. This corresponds to a 60° phase difference.

[0028] Calculate the independent phases of the k-th chaotic carrier wave using the following formula. This forms an independent phase sequence: During the i-th clock cycle, the instantaneous phase difference between two adjacent chaotic carriers k and k+1 is: S The above derivation proves that the phase difference depends only on a fixed digital offset, and not on the frequency control word at the current moment. It is irrelevant. Therefore, regardless of how the chaotic signal drives it... Random switching is performed, and the phase difference of the 6 carrier waves is always locked at 60°, thus strictly ensuring the natural sampling balance and harmonic cancellation characteristics of the cascaded H-bridge under frequency conversion conditions. The unipolar frequency multiplication CPS-PWM principle of the three-unit cascaded H-bridge is as follows: Figure 4 As shown.

[0029] Finally, the independent phase sequences generated by the above steps are essentially linearly growing sawtooth wave sequences, which need to be converted into symmetrical triangular carriers required by SPWM through a phase folding algorithm.

[0030] In this embodiment, the independent phase sequence output by the 32-bit phase accumulator is extracted. The high W bits are used as index data It is acceptable W =11, The range of values ​​is That is, [0, 2047], with the midpoint of the interval... The amplitude value of a symmetrical triangular carrier wave is defined by the boundary. The mapping logic is as follows: When index data When the index data is within the range [0, 1023], the output increases linearly with the input, generating the first half-cycle of a triangular carrier wave; when the index data... When the input is within the range [1024, 2047], the output decreases linearly with the input, generating the second half-cycle of the triangular carrier. Through this phase folding method, the system converts the monotonically increasing 11-bit sawtooth wave data stream into a 10-bit symmetrical triangular carrier with an amplitude between [0, 1023] in real time, with extremely low logic delay, strictly meeting the synchronization requirements of multiple carriers.

[0031] Step 4: Modulate the generated 6 symmetrical triangular carrier waves with unipolar frequency doubling SPWM modulation: Each H-bridge power unit corresponds to 2 chaotic carrier waves with a 180° phase difference. Compare the instantaneous values ​​with the sinusoidal modulation wave to generate complementary drive PWM pulses for the 4 switching devices of the H-bridge. The switching frequency of the power devices is related to the frequency of the chaotic carrier waves. Completely identical, the three-unit cascaded structure generates a total of 12 switching transistor control pulses to realize chaotic carrier phase-shift modulation of the cascaded H-bridge power amplifier.

[0032] Appendix Figure 6 This is a schematic diagram of a unipolar frequency-doubled CPS-PWM circuit with three cascaded H-bridge units. For a single cascaded unit, unipolar frequency-doubled modulation is used, and its principle is as follows: Figure 5 As shown. The principle of unipolar frequency multiplication CPS-PWM is based on unipolar frequency multiplication modulation, and by phase shifting the triangular carrier, the phase difference between adjacent cascaded units is made to be π / 3, that is, six carriers. The phase difference between i=1,2,3,4,5,6 is 60°. Using this phase difference, the output voltage pulse waveforms of each cascaded unit in the power amplifier can have a phase difference, and the superposition of these phases results in a seven-level voltage.

[0033] in, and These are a pair of triangular carrier waves with a 180° phase difference and the same amplitude, forming a single-unit modulation pair in a cascaded H-bridge power amplifier. They are also modulated by a sinusoidal signal. Instantaneous value comparison yields complementary switching transistor drive signals, driving the attached transistor... Figure 4 The two sets of switching transistors S5, S6 and S7, S8; similarly, and This is a pair of carrier waves in unit three of the power amplifier, simultaneously modulated by a sinusoidal signal. Complementary switching transistor drive signals are obtained by comparing instantaneous values, which drive the two sets of switching transistors S9, S10 and S11, S12 in the diagram. The cascaded H-bridge power amplifier of this invention has three units, but the chaotic carrier phase-shift modulation method proposed in this invention is not limited to this and can be directly extended to any N-unit (N is a positive integer ≥2) cascaded H-bridge multilevel power amplifier system. For the N-unit cascaded topology, when using unipolar frequency doubling CPS-SPWM modulation, 2N chaotic triangular carriers need to be generated, with a fixed phase difference of 360° / (2N) between adjacent carriers; the Logistic chaotic frequency perturbation model, the DDS-based common phase accumulation and independent phase offset architecture, and the phase folding carrier generation algorithm of this invention are all fully applicable. After extension, the carrier phase difference can still be strictly locked during the frequency conversion process to ensure the harmonic cancellation and frequency doubling characteristics of the cascaded H-bridge, achieving consistent spread spectrum descrambling and high-fidelity output effects, and can flexibly adapt to the engineering application requirements of multiple scenarios.

[0034] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples. Various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is defined by the appended claims.

[0035] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Various modifications or variations that can be made by those skilled in the art without creative effort within the scope of the appended claims are still within the scope of protection of the present invention.

Claims

1. A carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier, characterized in that... Includes the following steps: Step 1: Generate a chaotic modulation sequence based on the Logistic chaotic mapping, and introduce random perturbations to calculate the chaotic carrier frequency corresponding to each carrier period; Step 2: Based on the chaotic carrier frequency, the independent phase sequence of the chaotic carrier corresponding to each cascaded unit is generated by using the common phase accumulation and independent phase offset method, thereby generating each symmetrical triangular carrier that meets the requirements of the predetermined modulation strategy. Step 3: Modulate each symmetrical triangular carrier wave according to the predetermined modulation strategy to generate PWM control pulses for the corresponding cascaded H-bridge power unit switching devices.

2. The carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier according to claim 1, characterized in that: In step two, firstly, based on the chaotic carrier frequency, the corresponding frequency control word is generated using the Direct Digital Synthesis (DDS) principle. Then, based on the frequency control word, a common phase accumulator is constructed to generate a reference phase sequence shared by all cascaded units. Next, a fixed digital phase offset is constructed, and combined with the reference phase sequence, an independent phase sequence corresponding to the chaotic carrier of each cascaded unit is generated. Finally, through a phase folding algorithm, the sawtooth waves corresponding to the independent phase sequences of each cascaded unit are converted into symmetrical triangular carriers, resulting in multiple chaotic carriers with constant phase difference and synchronous chaotic frequency changes.

3. The carrier phase-shift modulation method for the cascaded H-bridge multilevel power amplifier according to claim 2, characterized in that: Suppose the cascaded H-bridge multilevel power amplifier consists of N cascaded units, corresponding to 2N symmetrical triangular carrier waves. The independent phases of the k-th chaotic carrier wave are calculated using the following formula. These, in turn, form independent phase sequences; in, This represents the reference phase within the i-th clock cycle. This represents the digital phase offset corresponding to the k-th chaotic carrier wave; The digital phase offset is calculated using the following formula. , Where k is the carrier index, k=0,1,...,2N 1; The bit width of the DDS phase accumulator and the full-scale range of the phase accumulator. Corresponding to a 360° phase.

4. The carrier phase-shift modulation method for the cascaded H-bridge multilevel power amplifier according to claim 3, characterized in that: The frequency control word is calculated using the following formula. : in, This indicates the bit width of the DDS phase accumulator. Indicates the system clock frequency. This represents the chaotic carrier frequency corresponding to the nth carrier period; The two adjacent terms in the reference phase sequence satisfy the following difference equation: in, This represents the reference phase during the i-th clock cycle.

5. The carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier according to claim 4, characterized in that: The predetermined modulation strategy is set to a unipolar frequency doubling CPS-PWM modulation method.

6. The carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier according to claim 1, characterized in that: In step one, the formula for calculating the chaotic carrier frequency is as follows: In the formula, This represents the chaotic carrier frequency corresponding to the nth carrier period. Indicates the reference carrier frequency. Indicates the frequency offset. Indicates the depth of the spread spectrum random perturbation. This represents the chaotic state variables in the chaotic modulation sequence generated by the Logistic chaotic mapping.

7. The carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier according to claim 6, characterized in that: In step one, the iterative formula for the Logistic chaotic mapping is as follows: In the formula, This represents the chaotic state variable in the nth iteration. This represents the bifurcation parameter of the Logistic chaotic mapping.

8. The carrier phase-shift modulation method for a cascaded H-bridge multilevel power amplifier according to claim 7, characterized in that: The bifurcation parameters The value range is 3.57~4.

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