Power electronic converter carrier-free spread spectrum energy and information coherence method based on pulse width modulation

Abstract

The invention discloses a carrier-free spread spectrum energy and information comodulation method for a power electronic converter based on pulse width modulation, which comprises the following steps of: performing direct baseband spread spectrum modulation on a PWM (Pulse Width Modulation) carrier period while performing power modulation by utilizing voltage or current change caused by a power switching device in a switching action process; and meanwhile, performing sequence position modulation on code element data, and realizing energy and information coordinated regulation and control of the power electronic converter by regulating interval time of two continuous sequences to represent data. The method has wide applicability, is not only suitable for various DC-DC converters based on PWM modulation, but also can be popularized to DC-AC and AC-DC converters.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic equipment communication, and in particular relates to a method for coherent modulation of energy and information of a power electronic converter without carrier spread spectrum based on pulse width modulation. Background Art

[0002] With the rapid development of new energy applications and network communication technologies, the power system is accelerating its transformation and upgrading towards an energy Internet dominated by new energy. In this process, a large number of power electronic equipment of different types and voltage levels are continuously connected to the power system, which significantly increases the complexity and management difficulty of the system. In response to this challenge, the Power / Signal Dual Modulation (PSDM) technology, which uses the inherent characteristics of power electronic equipment for information transmission, has emerged as an efficient means to improve the intelligence level of the system. Compared with traditional independent communication methods, PSDM technology organically integrates the power system and the information system, which not only significantly saves the cost of communication equipment and cables, but also has multiple functions such as power path identification, equipment status monitoring and fault diagnosis, providing new technical support for the efficient operation of the power system.

[0003] At present, the converter technologies for achieving signal coherence mainly include the PSDM-ESC method based on encoded switching carrier (ESC) and the PSDM-ECR method based on encoded control ripple (ECR). For example, the literature [R.Wang, Z.Lin, J.Du, J.Wu, and X.He, "Direct sequence spread spectrum-based PWM strategy for harmonic reduction and communication," IEEE Trans.Power Electron., vol.32, no.6, pp.4455–4465, Jun.2017] proposed a PSDM-ESC method based on direct sequence spread spectrum, which realizes information transmission through phase modulation of switching ripple; the literature [J.Chen, J.Wu, K.Liu, R.Wang, W.Li and X.He,"Improved Switching Ripple Modulation Strategy for Simultaneous Power Conversion and Data Communication in DC–DC Converters," IEEE Trans.Power Electron., vol.37, no.8, pp.9275-9284, Aug.2022] proposed an improved PSDM-ESC method by changing the switching ripple frequency to achieve DPSK modulation; the literature [Y.Zhu, J.Wu, R.Wang, Z.Lin and X.He,"Embedding Power Line Communication in PhotovoltaicOptimizer by Modulating Data in Power Control Loop," IEEE Trans.Ind.Electron., vol.66, no.5, pp.3948-3958, May 2019] injects the modulated signal as a disturbance into the control loop and proposes a PSDM-ECR method based on PSK modulation. In addition, the Chinese invention patent with publication number CN112994419B provides a composite modulation method of pulse width modulation and orthogonal frequency division multiplexing modulation based on the above theory and orthogonal frequency division multiplexing (OFDM) technology, achieving a breakthrough in coding efficiency and significantly improving the communication rate of the PSDM-ECR method.

[0004] However, the above documents and patents all rely on open-loop ripple or low-frequency disturbance as data carriers, which have the defects of limited bandwidth and insufficient communication capacity, and are vulnerable to external interference and attacks. In addition, the application scope of these methods is relatively limited, only applicable to DC / DC converters, and difficult to expand to AC / DC or DC / AC converters, thus limiting their actual promotion value. Summary of the invention

[0005] In view of the above, the present invention provides a carrier-free spread spectrum energy and information synchronization method for a power electronic converter based on pulse width modulation. On the basis of maintaining the duty cycle to control the output power, the PWM carrier signal is directly baseband spread spectrum modulated, and the voltage or current mutation signal generated at the moment of power switch switching is utilized to realize the energy and information synchronization modulation of the power electronic converter.

[0006] A method for coordinating energy and information of a power electronic converter without carrier spread spectrum based on pulse width modulation, specifically: a converter as a data transmitting end realizes energy transmission by adjusting the duty cycle to control the output power, sends the code element signal after spread spectrum processing by changing the switching cycle, and adopts sequence position modulation for the data, that is, the transmission interval time between two adjacent code elements is adjusted to represent the data to realize information transmission; a converter as a data receiving end is connected in parallel with the data transmitting end on the same AC bus, and the converter samples the voltage or current signal on the AC side, and then demodulates the obtained sampled signal to restore the corresponding data.

[0007] Furthermore, the symbol signal is composed of a plurality of continuous symbols, each symbol is represented by a spread spectrum sequence composed of N continuous binary chips, N is a natural number greater than 1; the transmission duration of each chip is a switching cycle, and when the chip value is 0, the switching cycle is selected as T 0 ; When the chip value is 1, the switching period is selected as T 1 .

[0008] Furthermore, the specific implementation method of the sequence position modulation is: setting M consecutive time intervals corresponding to digital codes from 0 to M-1, where M is a natural number greater than 1; adjusting the transmission interval time between two adjacent code elements to represent M-ary data, if the transmission interval time falls within a certain time interval, the digital code corresponding to the interval is the digital code of the corresponding bit in the M-ary data.

[0009] Furthermore, the spread spectrum sequence may be a PN code sequence, a Gold code sequence, a Kasami code sequence, a Barker code sequence, or the like.

[0010] Furthermore, the data receiving end samples and demodulates the voltage or current signal on the AC side after the switch of the converter at the data sending end is actuated (turned on or off).

[0011] Furthermore, the specific process of the data receiving end demodulating the sampled signal is as follows:

[0012] (1) Sampling the voltage or current signal on the AC side of the data receiving converter, with a sampling interval of T ad ;

[0013] (2) Use the sliding window to perform feature operations on the sampled signal and calculate the corresponding feature signal;

[0014] (3) performing despreading operation on the characteristic signal segment by segment to obtain the despreading value of each segment;

[0015] (4) For the despread value of any segment, if it is greater than the set threshold and greater than the despread values ​​of the previous K segments, the start time of the segment corresponding to the despread value is marked as the time when the current valid code element is received and recorded as T r1 , K is a natural number and 1<K<L / 2;

[0016] (5) The time when the last valid code element was received is recorded as T r2 , calculate the time interval T between two code element receptions d =T r1 -T r2 ;

[0017] (6) Determine T d The time interval in which the digital code corresponds to the interval is the digital code of the corresponding bit in the M-ary data.

[0018] Furthermore, in step (2), the characteristic signal is calculated by the following formula:

[0019]

[0020] Where: y(i) is the i-th eigenvalue in the characteristic signal, d(j) is the sliding window D i Where, the sampling value at the end of the switching cycle corresponding to the jth code chip, i is a natural number.

[0021] Furthermore, the sliding window D i The length of is L+1, which includes the i-th sample value in the sampled signal and its previous L sample values, L=T code / T ad , T code is the symbol period (the sum of the transmission durations of all chips in the spread spectrum sequence).

[0022] Furthermore, the despreading operation in step (3) may be performed by effective value calculation, discrete Fourier operation or wavelet transform operation.

[0023] The method of the present invention realizes synchronous modulation of power and information by adjusting the PWM carrier signal, which can effectively solve the shortcomings of the existing PSDM technology in bandwidth, communication capacity and scope of application; the method realizes data transmission by adjusting the switching cycle, and at the same time improves the efficiency of information transmission by using sequence position modulation, which is particularly suitable for various types of power electronic converters, not only expanding the application scenarios, but also improving the anti-interference ability. Compared with the traditional technology that relies on switching ripple or low-frequency disturbance, the present invention realizes more efficient and reliable data transmission, and has broad application prospects in the fields of smart grid and new energy.

[0024] In addition, the method of the present invention reduces the need for additional communication equipment by combining direct baseband spread spectrum modulation and energy transmission, thereby reducing system costs and having greater flexibility and scalability; especially in complex power systems, it can realize functions such as equipment status monitoring and fault diagnosis, thereby further improving the intelligence and automation level of the power system, and has significant technical advantages and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of code element sequence.

[0026] Figure 2 Schematic diagram of the calculation principle of the eigenvalue y(i).

[0027] Figure 3 Schematic diagram of data demodulation.

[0028] Figure 4 This is a schematic diagram of the full-bridge inverter grid-connected circuit structure.

[0029] Figure 5 Schematic diagram of the inverter SPWM signal generation mechanism. DETAILED DESCRIPTION

[0030] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0031] The present invention discloses a carrier-free spread spectrum signal synchronization method for a power electronic converter based on pulse width modulation, which realizes information transmission by changing the switching cycle on the basis of realizing output voltage or current control by adjusting the duty cycle of the power electronic converter.

[0032] The power electronic converter sends a spread spectrum processed code element signal by changing the switching cycle, where each code element is a spread spectrum sequence composed of N consecutive binary code chips, and each code chip corresponds to a switching cycle, such as Figure 1 As shown, when the chip value is 0, the switching period is T 0 ; When the chip value is 1, the switching cycle is T 1The chip sequence may be a PN code (pseudo-random noise code), a Gold code, a Kasami code or a Barker code.

[0033] At the data receiving end, data decoding is performed by measuring the voltage or current disturbance signal generated by the power electronic converter at the power input side, output side or ground terminal within a specific time after the power electronic converter is turned on or off. The data is modulated by sequence position, that is, the data is represented by adjusting the interval time between two consecutive sequences. The receiving end uses the following steps for decoding:

[0034] (1) Use high-speed AD to sample the signal with a sampling interval of T ad , saved as an array d(n), the array length is L+1, where L is a code element period T code The number of sampling points, that is, L = T code / T ad , the newly received data is stored as d(L), and the first data is d(0).

[0035] (2) Figure 2 As shown, the sampled data is despread:

[0036]

[0037] Where: y(i) is the i-th eigenvalue in the characteristic signal, d(j) is the sliding window D i Where, the sampling value at the end of the switching cycle corresponding to the jth code chip, i is a natural number.

[0038] (3) y(i) is calculated immediately after each AD sampling, and then the y(i) sequence is subjected to effective value, discrete Fourier transform or wavelet transform operation over a period of time to obtain Y(k), as follows: Figure 3 As shown; Y(k) and a threshold R TH In comparison, if it is greater than the threshold and greater than the first K data, Then mark the time when the code element is received as T r1 .

[0039] (4) The time when the last valid code element was received is recorded as T r2 , calculate T d =T r1 -T r2 .

[0040] (5) Set N intervals, respectively {L 0 ,L 1},{L 1 ,L 2},…,{L N-1 ,L N By comparing T dThe value of , determine its interval: if it satisfies L i-1 <T d <L i , the corresponding data is i.

[0041] Example

[0042] Next we will Figure 4 Taking the full-bridge inverter circuit shown in FIG. 1 as an example, in this implementation scheme, a two-stage full-bridge inverter circuit is used to realize data transmission and reception. The two inverters work in parallel and respectively assume different functions. Inverter 1 is used as the data transmission end and inverter 2 is used as the receiving end. The full-bridge inverter circuit is one of the common power electronic circuits. It can adjust the current and voltage waveforms by controlling the conduction and shutdown of the switch tube, thereby realizing the conversion of electric energy; each inverter is composed of four switch tubes (Q1, Q2, Q3, Q4), and their working states are controlled by pulse width modulation (PWM) signals.

[0043] In this embodiment, the switching signal of the inverter is provided by a bipolar modulated SPWM (sinusoidal pulse width modulation) signal, Q1 and Q3 of the inverter 1 are controlled by the same SPWM signal, and the control signals of Q2 and Q4 are complementary signals of the Q1 and Q3 signals. The advantage of bipolar modulation is that it can effectively reduce electromagnetic interference during the switching process, and at the same time, while ensuring efficient transmission, it reduces heat generation and improves the overall working efficiency of the inverter.

[0044] Inverter 1 is used as the data transmitter, with a reference sine wave frequency of 50 Hz, and a sawtooth wave as the power carrier signal. By adjusting the period of the sawtooth wave, the code element signal after spread spectrum processing is sent. In this embodiment, each code element sequence is composed of a spread spectrum sequence composed of N consecutive binary code chips, and each code chip corresponds to a switching cycle, such as Figure 5 As shown, when the chip value is 0, the switching period selects T 0 =10us; when the chip value is 1, the switching cycle selects T 1 =9us; in this way, inverter 1 transmits spread spectrum processed digital information in its switching cycle. The spread spectrum sequence expands the signal in the time domain and increases the spectrum width of the signal; the selection of the spread spectrum sequence will directly affect the anti-interference ability of the system, the demodulation performance of the signal and the real-time performance of the system. Common spread spectrum sequences include PN code, Gold code, Kasami code and Barker code. This embodiment selects a 31-bit PN code as the spread spectrum sequence for data modulation. The PN code has good autocorrelation and is easy to implement. It is very suitable for use in power electronic systems such as inverters. By spread spectrum modulation of the signal, the PN code can not only effectively improve the anti-interference ability, but also improve the signal quality and stability of the system. The following is a detailed introduction on how to generate and apply a 31-bit PN code.

[0045] PN code is a pseudo-random sequence generated by a linear feedback shift register (LFSR). LFSR can generate pseudo-random sequences through simple feedback and shift operations, which is efficient and feasible. In order to ensure the anti-interference ability of the signal, we chose a PN code with a maximum length of 31 bits, which can provide a good spread spectrum effect.

[0046] The characteristic of the 31-bit PN code is that its period is long (2 31 -1 code element), and has good autocorrelation, suitable for complex power electronic environments, and can effectively resist noise interference and signal attenuation. The generation of PN code is carried out through the feedback mechanism of LFSR, and the specific generation process is as follows:

[0047] The generation of the 31-bit PN code is based on a 31-bit LFSR, whose feedback polynomial is:

[0048] A(x)=x 31 +x 28 +x 25 +x 24 +1

[0049] This polynomial represents the feedback structure used in LFSR. The working method of LFSR is to first initialize the LFSR register and set the initial state (non-zero initial value, such as all 1 or all 0). Each time it shifts, a new feedback bit is calculated through an XOR operation and inserted into the lowest bit of the register; the value output each time is a bit of the PN code until a 31-bit PN code sequence is generated.

[0050] The formula is:

[0051] feedback(t) = x 31 ⊕x 28 ⊕x 25 ⊕x 24

[0052] Where: x 31 ⊕、x 28 ⊕、x 25 ⊕、x 24 ⊕ are bits 31, 28, 25, and 24 in the LFSR register respectively.

[0053] After each shift, the LFSR state is updated until the PN code sequence generates a complete 31 bits; the generated sequence is pseudo-random and can meet the requirements of spread spectrum modulation.

[0054] In this embodiment, a 31-bit PN code sequence is used to modulate the power carrier signal of the inverter 1. In each symbol period, the PN code sequence is used to adjust the cycle length of the inverter switch, thereby achieving signal spread spectrum. Specifically, in each spread spectrum period, each bit of the PN code sequence corresponds to a switching period; when the chip value is 0, the switching period selects T 0 =10us; when the chip value is 1, the switching cycle selects T 1 =9us.

[0055] Inverter 2, as the data receiving end, completes data reception and demodulation by measuring the voltage or current disturbance signal of the power electronic converter after the switching action. In order to ensure efficient data transmission and high accuracy, the receiving end adopts precise signal processing algorithms, including high-speed sampling, despreading operation, frequency domain processing and feature extraction.

[0056] (1) High-speed sampling and data storage

[0057] The receiving end uses a high-speed analog-to-digital converter (ADC) to match the transformer T 2 The mutual inductance voltage u 2 The signal is sampled with a sampling interval of T ad The sampling interval should be small enough to ensure the timeliness and accuracy of the sampled data. The sampling frequency should be at least twice the signal bandwidth, usually up to several MHz. The sampled values ​​are stored in an array d(n) with an array length of L+1, where L is a symbol period T code The number of sampling points.

[0058] (2) Despreading operation

[0059] The receiving end performs despreading on the sampled data, extracts the characteristic signal through the sliding window technology, and calculates the characteristic value y(i):

[0060]

[0061] Where: d(j) is the sliding window D i Wherein, the sampling value at the end of the switching cycle corresponding to the jth code chip, i is a natural number; by weighted summing the sampling values, the characteristic information of the signal can be obtained, which provides a basis for subsequent data demodulation.

[0062] (3) Data processing and effective value calculation

[0063] After each AD sampling, y(i) is calculated immediately, and then the y(i) sequence is further processed. Common processing methods include calculating the effective value, discrete Fourier transform (DFT) or wavelet transform (WT). These processing methods can transform from the time domain to the frequency domain, extract key information from the signal, and thus improve the demodulation accuracy of the signal. The despread value Y(k) is obtained by processing, and Y(k) will be compared with the preset threshold R TH If Y(k) is greater than the threshold and greater than the previous K data (i.e., to ensure that the signal is strong enough to avoid false detection), the time when the code element is received is marked as T r1 , where K is a window parameter, which is set to a value less than L / 2 to ensure that the first K data points do not have too much impact on the current signal, thereby avoiding the influence of signal interference on the reception result.

[0064] (4) Symbol Time Marking and Decoding

[0065] When a valid code element is received, the time is marked as T r1 Then, record the time T when the last valid code element was received r2 , and calculate the symbol interval T d =T r1 -T r2 , as the basis for decoding.

[0066] In order to further determine the transmitted data, the receiving end divides the symbol interval T d Compare with the preset N intervals, the intervals are set as:

[0067] {L 0 ,L 1},{L 1 ,L 2},…,{L N-1 ,L N}

[0068] By judging T d Specifically, if L i-1 <T d <L i , it means the received data is i.

[0069] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for coherent energy and information of a power electronic converter without carrier spread spectrum based on pulse width modulation, characterized in that: The converter as the data sending end realizes energy transmission by adjusting the duty cycle to control the output power, sends the code element signal after spread spectrum processing by changing the switching period, and adopts sequence position modulation for the data, that is, the transmission interval time between two adjacent code elements is adjusted to represent the data to realize information transmission; the converter as the data receiving end is connected in parallel with the data sending end on the same AC bus, and the converter samples the voltage or current signal on the AC side, and then demodulates the obtained sampled signal to restore the corresponding data.

2. The method for coherent energy and information of a power electronic converter without carrier spread spectrum according to claim 1, characterized in that: The symbol signal is composed of a plurality of continuous symbols, each symbol is represented by a spread spectrum sequence composed of N continuous binary chips, N is a natural number greater than 1; the transmission duration of each chip is a switching cycle, when the chip value is 0, the switching cycle is selected as T0; When the chip value is 1, the switching period is selected as T1.

3. The method for coherent energy and information of a power electronic converter without carrier spread spectrum according to claim 2, characterized in that: The specific implementation method of the sequence position modulation is: set M consecutive time intervals corresponding to digital codes from 0 to M-1, where M is a natural number greater than 1; adjust the transmission interval time between two adjacent code elements to represent M-ary data, and if the transmission interval time falls within a certain time interval, the digital code corresponding to the interval is the digital code of the corresponding bit in the M-ary data.

4. The method for coherent energy and information of a power electronic converter without carrier spread spectrum according to claim 2, characterized in that: The spread spectrum sequence adopts a PN code sequence, a Gold code sequence, a Kasami code sequence or a Barker code sequence.

5. The method for coherent energy and information of a power electronic converter without carrier spread spectrum according to claim 1, characterized in that: The data receiving end samples and demodulates the voltage or current signal on the AC side after the switch of the converter at the data sending end is actuated.

6. The method for coherent energy and information of a power electronic converter without carrier spread spectrum according to claim 3, characterized in that: The specific process of demodulating the sampling signal at the data receiving end is as follows: (1) Sampling the voltage or current signal on the AC side of the data receiving converter, with a sampling interval of T ad ; (2) Use the sliding window to perform feature operations on the sampled signal and calculate the corresponding feature signal; (3) performing despreading operation on the characteristic signal segment by segment to obtain the despreading value of each segment; (4) For the despread value of any segment, if it is greater than the set threshold and greater than the despread values ​​of the previous K segments, the start time of the segment corresponding to the despread value is marked as the time when the current valid code element is received and recorded as T r1 , K is a natural number and 1<K<L / 2; (5) The time when the last valid code element was received is recorded as T r2 , calculate the time interval T between two code element receptions d =T r1 -T r2 ; (6) Determine T d The time interval in which the digital code corresponds to the interval is the digital code of the corresponding bit in the M-ary data.

7. The method for coherent energy and information of a power electronic converter without carrier spread spectrum according to claim 6, characterized in that: In the step (2), the characteristic signal is calculated by the following formula: Where: y(i) is the i-th eigenvalue in the characteristic signal, d(j) is the sliding window D i Where, the sampling value at the end of the switching cycle corresponding to the jth code chip, i is a natural number.

8. The method for coherent energy and information of a power electronic converter without carrier spread spectrum according to claim 7, characterized in that: The sliding window D i The length of is L+1, which includes the i-th sample value in the sampled signal and its previous L sample values, L=T code / T ad , T code is the symbol period.

9. The method for coherent energy and information of a power electronic converter without carrier spread spectrum according to claim 6, characterized in that: The despreading operation in step (3) adopts effective value calculation, discrete Fourier operation or wavelet transform operation.

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