DC-AC converter energy and information simultaneous transmission method based on direct-axis component demodulation

Abstract

The invention relates to the technical field of power electronics and communication, in particular to a DC-AC converter energy and signal simultaneous transmission method based on direct-axis component demodulation, which comprises the following specific steps of: selecting different zero vector positions according to information code elements required to be transmitted, generating PWM (Pulse Width Modulation) carrier waves embedded with information, sampling a line voltage, inputting the line voltage into a phase-locked loop, performing Park conversion and then outputting a direct-axis component, setting passband parameters of the digital band-pass filter, extracting components of sideband harmonics on a direct axis within a switching frequency setting range and solving an absolute value to obtain an amplitude of a direct-axis component, correcting clock delay by using a synchronization algorithm, outputting a result integral value within a unit code element width, and performing zero clearing at a starting moment of a next code element; and setting a demodulation threshold according to the sampling rate and the integral output result, and comparing, judging and outputting demodulation information. By adopting the DC-AC converter energy and information simultaneous transmission method based on direct-axis component demodulation, high-bit-rate communication can be realized on the premise of low calculation complexity.

Description

Technical Field

[0001] This invention relates to the fields of power electronics and communication technology, and in particular to a method for simultaneous transmission of power and communication signals in a DC-AC converter based on direct-axis component demodulation. Background Technology

[0002] In modern power systems, communication systems are essential for improving the coordination between grid-connected equipment and promoting the intelligence and digitalization of the power system. However, both wired and wireless communication networks increase the installation and maintenance costs of communication equipment. Early power line communication (PLC) technology used couplers to superimpose information onto the power bus, making it a common channel for both energy and information flow, achieving simultaneous transmission of energy and information, eliminating the need for separate communication lines, and reducing costs. However, the couplers relied upon by PLC technology are bulky, difficult to install, and have high maintenance costs. In addition, the information signals injected through the coupling coils can damage power quality and even cause malfunctions in grid protection devices. Furthermore, the insulation requirements between the signal injection side and the grid side of the coupler are high, posing safety hazards.

[0003] To address the shortcomings of power line communication (PLC) technology, a simultaneous energy and information transmission technology based on the switching ripple of power electronic converters has been proposed. This technology modulates information and energy simultaneously during the switching process of the power switching transistors, embedding the information into the bus voltage switching ripple, which is then extracted at the demodulation end, achieving simultaneous energy and information transmission. This technology requires no additional coupler, resulting in low communication costs and minimal safety risks. Furthermore, in this switching ripple-based simultaneous energy and information transmission technology, the information modulation process and the energy modulation process are integrated, minimizing the damage to power quality compared to traditional PLC.

[0004] like Figure 8 The diagram illustrates a PWM carrier frequency shift keying (PWM keying) approach. During simultaneous signal and communication transmission, different symbols "0" and "1" correspond to different frequencies of PWM triangular carriers. By shifting the PWM carrier frequency, information is embedded in the switching signal and the motor cable. At the demodulation end, a current sensor samples the cable current, which is then processed by a high-pass filter, a differential amplifier, and a Schmitt trigger comparator to output the demodulated signal. This strategy uses two different frequency triangular carriers to randomly switch, introducing more switching harmonic components, which significantly degrades power quality.

[0005] like Figure 9The diagram illustrates a simultaneous transmission technology based on reference signal superposition. Information symbols are modulated into sinusoidal carrier signals of different frequencies using frequency shift keying (FSK) and then superimposed onto the outer voltage loop reference voltage. After the sinusoidal carrier participates in closed-loop control, the information is embedded in the switch drive signal and flows through an LC filter to another converter or the load side. The sampling circuit extracts the voltage information at the receiving end and demodulates the information through filters, envelope detectors, and threshold decision modules. However, this strategy relies on the control loop, constantly changing the reference signal, thus sacrificing the stability of the simultaneous transmission system.

[0006] In three-phase DC-AC converters, due to their complex topology and control methods, as well as the requirements for high grid-connected power quality and electromagnetic compatibility, the development of simultaneous power transmission and signal transmission technologies is limited. Currently, they are mainly divided into reference signal superposition and PWM carrier frequency shift keying methods. However, the reference signal superposition-based simultaneous power transmission strategy constantly changes the amplitude of the reference signal, thus posing a challenge to the closed-loop stability of the system. Furthermore, the superposition of the carrier signal introduces harmonic interference at the carrier frequency, impairing power quality. Similarly, in the PWM carrier frequency shift keying-based simultaneous power transmission strategy, the triangular carrier frequency and switching frequency constantly change, generating more switching harmonics during modulation, which has a significant impact on power quality.

[0007] Recently, several technologies have been developed for the simultaneous transmission of power and information between DC-AC converters, including zero-vector modulation (including zero-vector width and zero-vector position modulation) based on space vector pulse width modulation (SVPWM) control, and phase-shift keying modulation based on sinusoidal pulse width modulation (SPWM). In DC-AC converters, there are almost no harmonic components at the switching frequency; after modulation, the information is contained in the sideband harmonics near the switching frequency. Extracting this sideband harmonic information is a key challenge in the simultaneous transmission of power and information in DC-AC converters.

[0008] To extract information hidden in the harmonics of sideband frequencies, simultaneous communication based on variable-zero vector modulation often employs sliding FFT demodulation. However, the sliding FFT algorithm is not only computationally intensive but also limited by the resolution frequency. When the resolution accuracy of the sideband frequency is too high, the sampling rate must be increased and the width of the sliding window must be widened, thus limiting the communication bit rate.

[0009] In SPWM-based phase shift keying modulation, coherent carrier demodulation after multiple phase-locking operations is employed, such as... Figure 10As shown, the demodulation algorithm first preserves the sideband frequency components containing the information through bandpass filtering. After multiplication with a local coherent synchronization carrier at the switching frequency, the switching frequency components are eliminated by low-pass filtering. Next, after multiplication with a coherent carrier at three times the fundamental frequency, a second low-pass filtering is applied. Finally, phase information can be extracted from the envelope, thus demodulating the data. While this demodulation algorithm avoids using FFT, it requires phase-locking with both the fundamental and switching frequency carriers simultaneously. When noise is high, phase-locking with the high-frequency switching frequency carrier is difficult. Furthermore, after the second coherent multiplication, the high-frequency components are filtered out by the low-pass filter, leaving only a sine wave at three times the fundamental frequency (150Hz) as the information carrier. Because the final demodulated carrier frequency is relatively low, it is difficult to load high-bit-rate information, thus limiting the bit rate.

[0010] In summary, existing demodulation methods cannot achieve high bit rate communication with low computational complexity, thus there is an urgent need for an innovative demodulation scheme to overcome this bottleneck. Summary of the Invention

[0011] The purpose of this invention is to provide a DC-AC converter energy and signal transmission method based on direct-axis component demodulation. Based on zero-vector position modulation, by mapping the three-phase line voltage ripple to the direct-axis component and using energy integration decision, it fundamentally avoids the limitations of FFT calculation and frequency resolution, and provides a new technical path for achieving high bit rate and low complexity demodulation.

[0012] To achieve the above objectives, this invention provides a method for simultaneous transmission of energy and information in a DC-AC converter based on direct-axis component demodulation, the specific steps of which are as follows: Step S1: Select different zero vector positions according to the information symbols to be transmitted; generate a PWM carrier embedded with information based on the modulation of the variable zero vector position; Step S2: Sample the line voltage, input it into the phase-locked loop, perform Park transformation, and output the direct-axis component; Step S3: Set the passband parameters of the digital bandpass filter model, extract the components of the sideband harmonics on the direct axis within the switching frequency setting range, and calculate their absolute values ​​to obtain the amplitude of the direct axis components. Step S4: Perform bit synchronization operation, align the clocks of the demodulation end and the transmitter end to estimate the clock delay, and use a synchronization algorithm to iteratively correct the clock delay until complete synchronization; Step S5: Output the integral value of the result within the unit symbol width, and clear it to zero at the beginning of the next symbol. Step S6: Set the demodulation threshold, compare and determine, and output the demodulation information.

[0013] Preferably, in step S1, the PWM carrier generated by modulation based on the position of the zero vector is used. When the symbol "0" is sent, the zero vector is placed in the center of the switching cycle. When the symbol "1" is sent, the zero vector is shifted to the right from the center position. The position of the vertex of the triangular wave changes continuously with the information symbols.

[0014] Preferably, in step S2, the sampling of the three-phase line voltage needs to be done on the load side. A voltage sensor is used to measure the voltage between the three-phase output terminals, and the measured line voltage is then transformed by Park to obtain the direct-axis component of the three-phase line voltage. The rotation angle required for the transformation is provided in real time by the phase-locked loop.

[0015] Preferably, in step S3, the digital bandpass filter is used to filter out low-frequency fundamental components, switching noise, and other interference, and outputs sideband harmonic signals carrying information.

[0016] Preferably, the bit synchronization operation in step S4 is based on the amplitude of the direct-axis component to estimate the clock delay and achieve transmit and receive clock alignment. When the integration window of the receiving end is precisely aligned with the symbol window of the transmitting end, the integral value of the amplitude signal of the direct-axis component within a window reaches its maximum.

[0017] Preferably, in step S5, the width of the integral output window is selected as the unit symbol length; If the window width is less than the symbol width, it is impossible to collect all the energy of the symbol, the signal-to-noise ratio will decrease, and the decision will be unreliable. If the window width is greater than the symbol width, the integral value will include the energy of the current symbol and the energy of the beginning part of the next symbol. This will introduce inter-symbol interference, that is, the previous symbol will interfere with the decision of the next symbol, which will also greatly increase the bit error rate and make the decision unreliable.

[0018] Preferably, in step S6, a demodulation threshold is set based on the statistical distribution of the integral output results to minimize the bit error rate of the demodulated output information.

[0019] Therefore, the present invention employs the above-mentioned method for simultaneous transmission of information and power in a DC-AC converter based on direct-axis component demodulation, which has the following beneficial effects: (1) The demodulation computation of this invention is small, requiring only one phase-locking process for the fundamental frequency. It does not rely on the FFT algorithm, only requires absolute value calculation and ordinary integral output calculation, which is convenient to run on ordinary DSP microprocessors.

[0020] (2) The present invention has a high bit rate and short communication delay, which can meet the application requirements of more smart grid communication scenarios.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a demodulation flowchart of the present invention; Figure 2 The diagram shows the modulation strategy for simultaneous transmission of the signal "0" by varying the zero vector position. These are three pairs of complementary driving signals. The three corresponding modulation waves are calculated by the digital controller based on the voltage command. It is a seven-segment SVPWM sequence with zero vector. and The total action time is evenly distributed across the beginning, end, and middle of the switching cycle; Figure 3 The diagram shows the modulation strategy for simultaneous transmission of the signal symbol "1" with a zero-vector position, where... These are three pairs of complementary driving signals. The three corresponding modulation waves are calculated by the digital controller based on the voltage command. It is a seven-segment SVPWM sequence with zero vector. The total action time increases at the beginning of the switching cycle and decreases at the end; Figure 4 This is a diagram of a phase-locked loop (PLL). Figure 5 The following are waveforms of three-phase line voltage and line current under a communication bit rate of 2 kbps: (a) is a comparison waveform of transmitted data, embedded information PWM carrier, and demodulated data; (b) is the transmitted data waveform; (c) is the embedded information PWM carrier waveform; (d) is the line voltage waveform between phases a and b on the load side; (e) is the three-phase line voltage waveform; and (f) is the three-phase line current waveform. Figure 6 The demodulated waveforms are shown below, where (a) is the waveform of the transmitted data, (b) is the waveform of the three-phase line voltage, (c) is the waveform of the direct-axis component obtained by the Park transform, (d) is the waveform of the direct-axis component after filtering and extraction, (e) is the waveform after taking the absolute value of the filtered direct-axis component, (f) is the waveform of the integral output, and (g) is the waveform of the output demodulated data. Figure 7 Diagram of a point-to-point simultaneous interpretation system; Figure 8 This is a schematic diagram of the DC-AC converter energy and signal transmission technology based on PWM carrier frequency shift keying in the specification of this invention. Figure 9 This is a schematic diagram of the DC-AC converter energy and signal transmission technology based on the reference signal superposition method in the specification of this invention. Figure 10 This is a flowchart of a local coherent demodulation process for simultaneous transmission of energy and information based on SPWM modulation according to the present invention. Detailed Implementation

[0023] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0025] Example This invention provides a method for simultaneous transmission of energy and information in a DC-AC converter based on direct-axis component demodulation, the specific steps of which are as follows: Step S1: Select different zero vector positions according to the information symbols to be transmitted; generate a PWM carrier embedded with information based on the modulation of the variable zero vector position; Step S2: Sample the line voltage, input it into the phase-locked loop, perform Park transformation, and output the direct-axis component; Step S3: Set the passband parameters of the digital bandpass filter model, extract the components of the sideband harmonics on the direct axis within the switching frequency setting range, and calculate their absolute values ​​to obtain the amplitude of the direct axis components. Step S4: Perform bit synchronization operation, align the clocks of the demodulation end and the transmitter end to estimate the clock delay, and use a synchronization algorithm to iteratively correct the clock delay until complete synchronization; Step S5: Output the integral value of the result within the unit symbol width, and clear it to zero at the beginning of the next symbol. Step S6: Set the demodulation threshold, compare and determine, and output the demodulation information.

[0026] Step S1 involves generating a PWM carrier based on the zero-vector position modulation, such as... Figure 2 The diagram shows the modulation strategy for simultaneous transmission and reception of the signal "0" by varying the zero vector position. When transmitting the signal "0", the zero vector is placed at the exact center of the switching cycle. Figure 3The diagram shows the modulation strategy for simultaneous transmission and reception of the signal symbol "1" by shifting the zero vector position. When transmitting the signal symbol "1", the zero vector is shifted to the right from the center position. The position of the triangular wave vertex changes continuously with the information symbol.

[0027] In step S2, the sampling of the three-phase line voltage needs to be done on the load side. A voltage sensor is used to measure the voltage between the three-phase output terminals. The measured line voltage is then transformed using a Park transform to obtain the direct-axis components of the three-phase line voltage. The required rotation angle for the transformation is provided in real-time by a phase-locked loop. Figure 4 The diagram shown is a phase-locked loop structure diagram.

[0028] like Figure 1 As shown, Figure 1 This is a demodulation flowchart of the present invention, which fully illustrates the specific process of performing subsequent steps after the Park transformation outputs the direct-axis component in step S2.

[0029] In step S3, the digital bandpass filter is used to filter out low-frequency fundamental components, switching noise, and other interference, and outputs sideband harmonic signals that carry information.

[0030] The bit synchronization operation in step S4 is based on the amplitude of the direct axis component to estimate the clock delay and achieve clock alignment between the transmit and receive. When the integration window of the receiver is precisely aligned with the symbol window of the transmitter, the integral value of the amplitude signal of the direct axis component within a window reaches its maximum.

[0031] In step S5, the width of the integral output window is selected as the unit symbol length; If the window width is less than the symbol width, it is impossible to collect all the energy of the symbol, the signal-to-noise ratio will decrease, and the decision will be unreliable. If the window width is greater than the symbol width, the integral value will include the energy of the current symbol and the energy of the beginning part of the next symbol. This will introduce inter-symbol interference, that is, the previous symbol will interfere with the decision of the next symbol, which will also greatly increase the bit error rate and make the decision unreliable.

[0032] In step S6, a demodulation threshold is set based on the statistical distribution of the integral output results to minimize the bit error rate of the demodulated output information.

[0033] like Figure 5 The figure shows the waveforms of three-phase line voltage and line current at a communication bit rate of 2kbps. It can be seen that the differences in line voltage and line current under different symbol rates are not significant. For energy transmission, the voltage and current remain high-quality sine waves with low harmonic content, meeting grid connection requirements. This proves that the present invention causes almost no damage to power quality. Furthermore, information cannot be directly identified from these macroscopic waveforms; therefore, the demodulation method described in this invention is necessary. Figure 6As shown, the waveforms of the demodulation process of this invention are shown. It can be observed that the time width corresponding to each pulse of the integral output waveform is very short, and the integral output results still maintain a clear and distinguishable difference.

[0034] like Figure 7 The diagram illustrates a point-to-point energy and information transmission system, providing the application background and technical scenario of this invention. It consists of a three-phase DC-AC converter, an LCL filter, cables, a constant power load, and a demodulator. Information is modulated by zero-range vector position modulation (VZVPM) to generate a switch drive signal embedded with the information. The information flows through the LCL filter and the wiring (copper-based, using a type-type model), ultimately channeling both energy and information into the load. On the load side, voltage sensors measure the three-phase voltage, which is then output as a signal waveform by the demodulator.

[0035] As can be seen from this embodiment, the method described in this invention avoids the traditional sliding FFT calculation in principle, and reduces the computational complexity by adopting a new method without resolution constraints. It bypasses the frequency resolution bottleneck of FFT and achieves low computational complexity. Moreover, the traditional FFT demodulation method under the same modulation method has a communication bit rate of only 100 bits per second, while the method described in this invention achieves a communication bit rate of 2000 bits per second, which is a great improvement compared with the traditional method and realizes high bit rate communication.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for simultaneous transmission of information and power in a DC-AC converter based on direct-axis component demodulation, characterized in that, The specific steps are as follows: Step S1: Select different zero vector positions according to the information symbols to be transmitted; generate a PWM carrier embedded with information based on the modulation of the variable zero vector position; Step S2: Sample the line voltage, input it into the phase-locked loop, perform Park transformation, and output the direct-axis component; Step S3: Set the passband parameters of the digital bandpass filter model, extract the components of the sideband harmonics on the direct axis within the set switching frequency range, and calculate their absolute values ​​to obtain the direct axis components. The amplitude; Step S4: Perform bit synchronization operation, align the clocks of the demodulation end and the transmitter end to estimate the clock delay, and use a synchronization algorithm to iteratively correct the clock delay until complete synchronization; Step S5: Output the integral value of the result within the unit symbol width, and clear it to zero at the beginning of the next symbol. Step S6: Set the demodulation threshold, compare and determine, and output the demodulation information.

2. The method for simultaneous transmission of information and power in a DC-AC converter based on direct-axis component demodulation according to claim 1, characterized in that: In step S1, the PWM carrier generated by modulation based on the position of the zero vector is sent. When the symbol "0" is sent, the zero vector is placed in the center of the switching cycle. When the symbol "1" is sent, the zero vector is shifted to the right from the center position. The position of the vertex of the triangular wave changes continuously with the information symbol.

3. The method for simultaneous transmission of information and power in a DC-AC converter based on direct-axis component demodulation according to claim 2, characterized in that: In step S2, the sampling of the three-phase line voltage needs to be done on the load side. A voltage sensor is used to measure the voltage between the three-phase output terminals. The measured line voltage is then transformed by Park to obtain the direct-axis component of the three-phase line voltage. The rotation angle required for the transformation is provided in real time by the phase-locked loop.

4. The method for simultaneous transmission of information and power in a DC-AC converter based on direct-axis component demodulation according to claim 3, characterized in that: In step S3, the digital bandpass filter is used to filter out low-frequency fundamental components, switching noise, and other interference, and outputs sideband harmonic signals that carry information.

5. The method for simultaneous transmission of information in a DC-AC converter based on direct-axis component demodulation according to claim 4, characterized in that: The bit synchronization operation in step S4 is based on the amplitude of the direct axis component to estimate the clock delay and achieve clock alignment between the transmit and receive. When the integration window of the receiver is precisely aligned with the symbol window of the transmitter, the integral value of the amplitude signal of the direct axis component within a window reaches its maximum.

6. The method for simultaneous transmission of information and power in a DC-AC converter based on direct-axis component demodulation according to claim 5, characterized in that: In step S5, the width of the integral output window is selected as the unit symbol length.

7. The method for simultaneous transmission of information in a DC-AC converter based on direct-axis component demodulation according to claim 6, characterized in that: In step S6, a demodulation threshold is set based on the statistical distribution of the integral output results to minimize the bit error rate of the demodulated output information.

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