APF multi-machine parallel system current sharing control method and system and storage medium

Abstract

The application discloses an APF multi-machine parallel system current sharing control method and system, a storage medium, and an APF multi-machine parallel system, which is composed of N single-phase APFs connected in parallel to an electric network and is used for compensating for harmonic currents and reactive currents of the electric network; a signal generation module generates a data signal by using a modulation method of direct sequence spread spectrum differential phase shift keying (DS-DPSK); a signal acquisition and demodulation module is used for collecting, filtering, despreading and demodulating an electric network voltage signal and restoring the same into a corresponding data signal; and a compensation control module adjusts a compensation coefficient to realize current sharing control according to the received data information. The application can realize power quality treatment, data transmission, current sharing control for reducing inverter loss and safe and stable operation.

Description

Technical Field

[0001] This invention relates to the field of synchronous transmission of electrical energy and information, and in particular to a current sharing control method, system and storage medium for an APF multi-machine parallel system. Background Technology

[0002] Currently, we face the severe challenges of energy depletion and environmental pollution. Against this backdrop, there is a need to accelerate the construction of reliable and flexible active distribution networks and microgrids with widespread integration and interaction of various distributed energy sources. However, microgrids contain a large number of rectifier / inverter devices and nonlinear loads, which inevitably generate significant harmonics, severely degrading power quality and affecting grid connection safety. Therefore, it is urgent to suppress harmonics in microgrids.

[0003] Due to the intermittent nature of distributed power sources and frequent nonlinear load changes in microgrids, harmonic energy varies significantly. Traditional single active power filters (APFs) are no longer sufficient to meet the harmonic mitigation requirements of microgrids. Therefore, operating multiple small-capacity APFs in parallel is a practical approach. This method facilitates capacity expansion, provides fault redundancy, and offers advantages such as flexibility and high reliability. However, this scheme requires current-sharing control for each APF; otherwise, a single APF may operate under heavy load for extended periods, leading to premature aging and reduced system reliability. Furthermore, the resulting circulating current will increase system losses.

[0004] In recent years, most existing inventions and control methods for multi-machine parallel APF systems employ centralized control, as exemplified by patent applications CN111030113A and CN103311934A. This approach uses a dedicated control unit to handle tasks such as calculating current sharing and limiting coefficients, fault diagnosis, and troubleshooting. If this unit fails, the entire system becomes unusable, resulting in low system reliability. Furthermore, these control methods require additional communication equipment and lines, complicating control and hindering expansion and maintenance.

[0005] In a multi-APF (Active Power Filter) parallel system, uneven current distribution among the APFs can lead to circulating currents, increasing system losses, causing severe current distortion, and potentially damaging some APF units, thus reducing system reliability. Furthermore, operating under such uneven current distribution conditions for extended periods will result in significantly different aging rates for each APF, shortening the overall lifespan of the parallel system. Current technologies require additional communication modules and lines to achieve current sharing control across all APF outputs, increasing investment costs and reducing the system's scalability and flexibility due to the increased equipment requirements. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a current sharing control method, system and storage medium for a multi-APF parallel system, which can achieve communication control without adding additional communication equipment and communication lines, and ensure that the current compensation of each APF is uniform.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a current sharing control method for an APF multi-machine parallel system, comprising the following steps:

[0008] S1. Configure one APF as the host;

[0009] S2. Check if any new APF has been incorporated;

[0010] S3. If a new APF is added, the compensation coefficients of each existing APF are updated according to different methods depending on whether the relative position of the new APF is known; the compensation coefficients of the newly added APF are updated; return to step S2.

[0011] If no new APF is added, the master will query each slave APF sequentially at set intervals. If a slave does not respond to m queries at intervals of t1 seconds, the slave is determined to be faulty and disconnected. If the slave does not receive a query from the master within the set time, the master is determined to be faulty and disconnected, and the APF closest to the load side is selected as the new master. Each APF updates its current relative position information according to the disconnection command, then updates its own compensation coefficient, and returns to step S2.

[0012] This invention enables current sharing control of each APF, reducing circulating current and inverter losses, ensuring that each APF outputs the same power, and preventing any APF from aging faster due to long-term full-load operation. The method of this invention makes the entire system highly reliable and improves the lifespan of the multi-APF parallel system.

[0013] In step S1 of this invention, when multiple APFs are started simultaneously, the APF closest to the load side is set as the master; otherwise, the APF that starts first is the master.

[0014] In step S3 of this invention, the specific implementation process of updating the compensation coefficients of each connected APF in different ways according to whether the relative position of the new APF is known includes:

[0015] If the relative position of the APF to be merged is known, that is, the APF to be merged is in the APF n With APF n-1 When n=1, the APF to be incorporated is between APF1 and the load, then:

[0016] The APF to be merged sends a startup command;

[0017] Each connected APF receives the startup command. n APF n+1 ...APF N Updated to APF n+1 APF n+2 ..., APF N+1 The compensation coefficient K for each connected APF is calculated using the formula. dq : 1≤q≤N+1, where N is the total number of APFs;

[0018] The APF to be merged is updated to APF n Using formula K dn =1 / (N+2-n) gives the compensation coefficient K dn ;

[0019] If the relative position of the APF to be merged is unknown, then:

[0020] The APF to be connected detects the near-side load current and calculates the effective value of the harmonic current i. Ln-rms and send i Ln-rms Data information;

[0021] Each connected APF receives i Ln-rms Numerical information, and the locally detected effective value of harmonic current i Lm-rms Compare according to the formula Obtain n, the APF to be merged into is in APF n With APF n-1 The relative positions of the APFs to be incorporated are obtained from the relationships between them; the compensation coefficient K of each already incorporated APF is then calculated using the formula. dq : 1≤q≤N+1;

[0022] The host APF uses formula K to determine the relative position of the APF to be merged into. dn =1 / (N+2-n) Calculate and send the compensation coefficient K to be incorporated into the slave APF. dn The compensation coefficient information will be received and updated by the APF.

[0023] In step S3 of this invention, the specific implementation process of the host querying each slave APF includes:

[0024] 1) Source encoding is performed on the instruction information to obtain the information sequence. The instruction information is defined to consist of two parts: the first part is the 8-bit binary address of the APF; the second part is the start instruction, cut-off instruction, fault status code, compensation coefficient, and effective value of harmonic current.

[0025] 2) Perform convolutional channel coding on the information sequence to obtain the encoded binary sequence {a}.i}, 1≤i≤N1, where a i N1 represents the i-th bit of the binary sequence, with a value of 0 or 1; N1 represents the length of the information sequence.

[0026] 3) For {a i Differential encoding is performed to obtain the sequence to be sent, {d}. i},Right now Where a0 = 0, {d i The rate at which the sequence is converted into information is R. b The bipolar baseband signal d(t), i.e. d' i =2d i -1,g T (t) is a value with an amplitude of 1 and a width of T. b =1 / R b The rectangular pulse, where t represents the time independent variable of the DS-DPSK waveform, 0≤t≤T DS-DPSK T DS-DPSK The duration of the DS-DPSK waveform. Indicates the XOR operation;

[0027] 4) Spread spectrum modulation is performed on d(t) to obtain the signal to be transmitted, b(t), i.e., b(t) = d(t)·c(t); where c(t) is the information rate R. c The signal generated by the PN sequence signal generator {c i} is a PN sequence with values ​​of ±1, and p(t) is a sequence with an amplitude of 1 and a width of T. c =1 / R c A rectangular pulse, k = R c / R b Indicates the spreading factor;

[0028] 5) Pulse shape b(t) to obtain the modulated signal b'(t), b'(t) = b(t) * h(t); h(t) is the impulse response of the raised cosine roll-off filter; generate the DS-DPSK waveform s(t): s(t) = b'(t) * cos2πf c t;f c This is the cutoff frequency of the low-pass filter;

[0029] 6) Obtain the final transmitted signal s′(t) total ): s′(t total )=[s blank (t2),s LFM (t1),s blank (t2),s(t),s blank (t2),s LFM (t1),sblank (t2)]; t1∈[0,T LFM ], t1 is the time independent variable when calculating the linear frequency modulated wave, T LFM For the inserted linear frequency modulated wave s LFM The duration of (t1), f0 is the starting frequency of the linear frequency modulated wave, Δf is the frequency modulation frequency of the linear frequency modulated wave, and s blank (t2)=0,t2∈[0,T blank ], t2 is the time variable of the blank window, T blank For blank window s blank The duration of (t2), t total T is the time independent variable of the final single-carrier signal. total T is the total duration of a single-carrier signal. total =T DS-DPSK +2T blank +2T LFM .

[0030] The specific implementation process of the master querying each slave APF also includes:

[0031] A) Acquire the grid voltage signal, filter out noise interference outside the signal frequency band using a bandpass filter, and obtain the signal r(t) to be demodulated;

[0032] B) Combined with the length T of the LFM sync head LFM and the length T of the blank window blank The starting position τ0 of the acquired DS-DPSK waveform r(t) is: τ0 = τ max +T LFM +2T blank , τ max To make the linear frequency modulated signal s LFM (t) is the value of the independent variable when the correlation operation with the received signal takes the maximum correlation value;

[0033] C) r m Multiplying the local PN sequence signal c(t) (which is the same as that of the signal generation module) yields the despread data signal r'(t): r'(t) = r m (t)·c(t);

[0034] D) Delay r'(t) by one baseband signal period T. b Then multiply by r'(t) to achieve differential detuning:

[0035]

[0036] E) The above output result r'(t)·r'(t+T) b (through a cutoff frequency at f)c and 2f c A low-pass filter is used to filter out the second harmonic signal component, resulting in a preliminary demodulated signal.

[0037] F) The preliminary demodulated signal is sampled and decided, with the optimal sampling point located in the middle of the symbol. Sampling is then performed every symbol period. Sampling points with a decision value greater than 0 are determined as "0", and sampling points with a decision value less than 0 are determined as "1", thus obtaining the original information sequence {a}. i}

[0038] Also includes:

[0039] G) for {a i Perform maximum a posteriori (MAP) decoding on the convolutional code and select the bit with the maximum a posteriori probability as the received bit.

[0040] H) According to the rules in the information modulation process, the received bits are decoded. The first 8 received bits are decoded into the APF address, and the latter part of the received bits are decoded into the corresponding start command, switching command, fault status, compensation coefficient, and effective value of harmonic current.

[0041] When no new APF is incorporated, in step S3, the compensation coefficient K of each APF is... dp The updated formula is:

[0042]

[0043] As an inventive concept, the present invention also provides a current sharing control system for an APF multi-machine parallel system, comprising:

[0044] One or more processors;

[0045] A memory having stored one or more programs that, when executed by one or more processors, cause the one or more processors to implement the steps of the method described above.

[0046] As an inventive concept, the present invention also provides a computer-readable storage medium, characterized in that it stores a computer program, which, when executed by a processor, implements the steps of the method described above.

[0047] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention can be used in situations where multiple APFs need to be connected in parallel to jointly manage grid harmonics and reactive power. It eliminates the need for additional communication equipment and lines, adding data modulation signals to the compensation current command signal. Through SPWM, it achieves power quality management while simultaneously transmitting information, enabling current sharing control of each APF. This reduces circulating current and inverter losses, ensuring that each APF outputs the same power, preventing some APFs from aging rapidly due to uneven load operation, which would reduce the overall system reliability and lifespan. The DS-DPSK data modulation method ensures reliable information transmission. The current sharing control scheme employs master-slave control, eliminating the problem of "single-point failure equals global paralysis" inherent in centralized control, thus ensuring high reliability. Attached Figure Description

[0048] Figure 1 This invention relates to an APF multi-machine parallel system;

[0049] Figure 2 For single-phase command current i cN * Calculation process;

[0050] Figure 3 This is a control block diagram for generating a switching signal when only harmonic compensation is required in an embodiment of the present invention;

[0051] Figure 4 This is a control block diagram for generating switching signals when simultaneously compensating for harmonics and transmitting information, according to an embodiment of the present invention.

[0052] Figure 5 This is an embodiment of the information modulation process based on DS-DPSK.

[0053] Figure 6 This is the information demodulation process based on DS-DPSK in an embodiment of the present invention;

[0054] Figure 7 This is a flowchart of the flow sharing control method according to an embodiment of the present invention;

[0055] Figure 8 , Figure 9 The waveforms are: the fundamental reactive power difference between the two APFs, the fundamental reactive power waveforms of the two APFs, and the circulating current waveform, respectively, when the current sharing control of this embodiment is not implemented and when the current sharing control of this embodiment is implemented.

[0056] Figure 10 The diagram shows the power grid current waveforms before and after load compensation using an embodiment of the present invention.

[0057] Figure 11 This is a waveform diagram of the information demodulation process in an embodiment of the present invention. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] like Figure 1 As shown, the APF multi-machine parallel system includes N (N≥1) APFs connected in parallel to the power grid. Each APF has the same control unit, and all APF controllers include a compensation control module, a signal generation module, and a signal acquisition and demodulation module. For ease of description, based on the distance from the APF connection point to the load, they are sequentially named APF1, APF2, APF3, ... APF from closest to furthest. N . Figure 1 Middle U s L s For system power supply voltage and equivalent inductance; V G i G The mains voltage and mains current are given; harmonics and reactive current in the mains are generated by the inductive load L. L The H-bridge uncontrolled rectifier circuit provides the DC side (consisting of R, L, and C as shown in the diagram); i Lj i cj V dcj For APF j (1≤j≤N) Near-side load current, output compensation current, and DC-side capacitor voltage. An APF (Automatic Power Filter) is used to compensate for grid harmonics and reactive current; it includes an inverter and a filter inductor L. outj Inverter AC test via L outj Connect to the power grid, with a parallel support capacitor C on the DC side. dcj The inverter is an H-bridge circuit composed of IGBTs.

[0060] like Figure 2 As shown, this represents the single-phase command current i of the compensation control module. cj * Calculation process (Reference: Hou Pengfei, Yang Yuewen, Xu Haidong. An improved algorithm for reference current detection in a single-phase system [J]. Electrical Engineering, 2022, No.563(05):45-47+53.). Figure 2 in i Lj 'Near-side load current i acquired by current sensor Lj Multiply by the compensation coefficient K dj (K dj ≤1) is obtained; Figure 2 China V dcj *This is the DC-side reference voltage, and it is different from the actual voltage V. dcj The deviation is input to i through the PI controller. p The channel allows the inverter's output or absorbed power to include the fundamental active component, thereby maintaining the stability of the DC-side capacitor voltage. Switch S in the diagram... q Control whether reactive current compensation is performed; if it is disconnected, harmonics and reactive current are compensated simultaneously. i is calculated. cj * , with i cj The deviation is processed by a PI controller, and a grid voltage feedforward circuit is added to accelerate the current tracking response speed, ultimately obtaining a compensation command signal.

[0061] The APF compensation control module can enable the inverter to operate at two frequencies depending on whether information needs to be transmitted.

[0062] like Figure 3 As shown, when only grid harmonics and reactive current are compensated, the compensation control module compares the compensation command signal with the triangular carrier Φ1 (12.5kHz) to obtain a switching signal with a switching frequency of 12.5kHz.

[0063] like Figure 4 As shown, when information needs to be transmitted, the compensation control module superimposes the single-carrier communication waveform generated by the signal generation module onto the compensation command signal, compares it with the triangular carrier Φ2 (25kHz) to obtain a switching signal with a switching frequency of 25kHz, thereby realizing the output of compensation current carrying information.

[0064] Other APFs collect grid voltage V via voltage sensors. G The data is then processed by the signal acquisition and demodulation module to analyze V. G After digital filtering, demodulation, and sampling decision, the transmitted data information is obtained, realizing reliable information transmission; the compensation control module adjusts the compensation coefficient based on this information.

[0065] like Figure 5 As shown, the information modulation process based on DS-DPSK in this embodiment of the invention is as follows:

[0066] S1. Perform source coding on the instruction information. It is stipulated that the instruction information consists of two parts. The first part is the 8-bit binary address of the APF; the latter part of the information can be a start instruction, a cut-off instruction, a fault status code, a compensation coefficient, and the effective value of harmonic current. The latter part of the information is converted into a binary sequence according to the following rules: the start instruction is "1111 1111"; the cut-off instruction is "0000 0000"; the fault status code is a 12-bit binary sequence, and the user can customize the fault status information; the compensation coefficient is 1 / Z (0 < Z < 255, Z is an integer), convert Z into 8-bit binary, which is the compensation coefficient information; the effective value of harmonic current is rounded and converted into 16-bit binary, which is the effective value information of harmonic current.

[0067] S2. Perform convolutional channel coding on the information sequence to obtain the encoded binary sequence {a i}, 1 ≤ i ≤ N1, where a i represents the i-th bit of the binary sequence, taking values of 0 or 1; N1 represents the length of the information sequence.

[0068] S3. Perform differential coding on {a i} to obtain the sequence to be transmitted {d i}, that is

[0069]

[0070] where a0 = 0. Convert the sequence {d i} into a bipolar baseband signal d(t) with an information rate of R b , that is

[0071]

[0072] In the formula: d' i = 2d i - 1; g T (t) is a rectangular pulse with an amplitude of 1 and a width of T b = 1 / R b ; t represents the time independent variable of the DS-DPSK waveform, 0 ≤ t ≤ T DS-DPSK , T DS-DPSK is the duration of the DS-DPSK waveform, determined by the number of code elements and the baud rate.

[0073] S4. Perform spread spectrum modulation on d(t) to obtain the signal to be transmitted b(t), that is

[0074] b(t) = d(t)·c(t) (3)

[0075] where c(t) is the signal generated by a PN sequence signal generator with an information rate of R c , and is

[0076]

[0077] In the formula: {c i} is a PN sequence with values ​​of ±1; p(t) is a sequence with an amplitude of 1 and a width of T. c =1 / R c A rectangular pulse; k = R c / R b The spreading factor is a positive integer.

[0078] S5. Pulse shaping is performed on b(t) to obtain the signal to be modulated, b'(t). The roll-off factor α and the symbol duration T are set. c The impulse response h(t) of the raised cosine roll-off filter can be generated, and convolving it with b(t) yields the pulse shaper output b'(t):

[0079] b'(t)=b(t)*h(t) (5)

[0080] S6, Carrier Modulation. Set the carrier frequency f. c Generate DS-DPSK waveform s(t)

[0081] s(t)=b'(t)·cos2πf c t (6)

[0082] S7. Insert LFM synchronization header. Insert a specific duration T before the signal to be transmitted s(t). LFM linear frequency modulated wave t1∈[0,T LFM ], where t1 is the time independent variable when calculating the linear frequency modulated wave, T LFM For the inserted linear frequency modulated wave s LFM The duration of (t1) is given, where f0 is the starting frequency of the linear frequency modulated wave, and Δf is the modulation frequency of the linear frequency modulated wave; combined with a certain duration T. blank blank window blank (t2)=0,t2∈[0,T blank ], where t2 is the time variable of the blank window, T blank For blank window s blank The duration of (t2) is also shown; simultaneously, an LFM waveform is inserted at the end position of the signal to be transmitted s(t) to indicate the end of the signal, and finally the transmitted signal s′(t) is obtained. total ):

[0083] s′(t total )=[s blank (t2),s LFM (t1),s blank (t2),s(t),s blank (t2),sLFM (t1),s blank (t2)] (7)

[0084] Where t total T is the time independent variable of the final single-carrier signal. total T is the total duration of a single-carrier signal. total =T DS-DPSK +2T blank +2T LFM .

[0085] Figure 6 The DS-DPSK-based information demodulation process is shown below:

[0086] S1. The voltage sensor collects the grid voltage signal and filters out noise interference outside the signal frequency band through a bandpass filter to obtain the signal r(t) to be demodulated.

[0087] S2, Synchronously extract valid data segments r m (t). Combined with the length T of the LFM sync header. LFM and the length T of the blank window blank Then the starting position τ0 of the acquired DS-DPSK waveform r(t) can be obtained as follows:

[0088] τ0=τ max +T LFM +2T blank (8)

[0089] Where τ max To make the linear frequency modulated signal s LFM (t) is the value of the independent variable when the correlation operation with the received signal takes the maximum correlation value.

[0090] S3, De-expansion. (The r...) m The despread data signal r'(t) is obtained by multiplying it with the local PN sequence signal c(t) of the same signal generation module.

[0091] r'(t)=r m (t)·c(t) (9)

[0092] S4. Differential demodulation. Delay r'(t) by one baseband signal period T. b Multiplying this by r'(t) gives:

[0093]

[0094] In the formula: a' i =2a i -1,d'0=0. Pass the above output result through a cutoff frequency at f. c and 2fc By using a low-pass filter to filter out the second harmonic signal component, a preliminary demodulated signal can be obtained.

[0095] S5. Sampling and Decision. Low-pass filters are not ideal filters, so sampling and decision-making are required for the filter's output signal. The optimal sampling point is located in the middle of the symbol. Sampling is performed every symbol period thereafter. After decision-making, sampling points greater than 0 are classified as "0", and sampling points less than 0 are classified as "1". Finally, the original information sequence {a} is obtained. i}

[0096] S6, Channel decoding, error control. For {a i} The maximum a posteriori probability decoding of convolutional codes is performed (Lalit R.Bahl, John Cocke, Frederick Jelinek, Josef Raviv. Optimal decoding of linear codes for minimizing symbol error rate (Corresp.). [J]. IEEE Trans. Information Theory, 1974, 20(2)). In the decoding process, the bit with the maximum a posteriori probability is selected as the received bit, which can further ensure the reliability of communication.

[0097] S7. Source Decoding. According to the rules in the information modulation process, the received bits are decoded. The first 8 received bits are decoded into the APF address, and the remaining received bits can be decoded into information such as the corresponding start command, switching command, fault status, compensation coefficient, and effective value of harmonic current.

[0098] This system is based on master-slave control. Each APF uses the aforementioned DS-DPSK-based information modulation and demodulation method to transmit information such as start-up commands, switching commands, fault status, compensation coefficients, and effective values ​​of harmonic currents, and coordinates the control of the output current of each APF.

[0099] like Figure 7 As shown, the flow control method implemented in this system is as follows:

[0100] S1. Designate one APF as the master. When multiple APFs start simultaneously, the one closer to the load side becomes the master; otherwise, the one that starts first becomes the master. The purpose of selecting a master is to better facilitate information transmission and update compensation coefficients. There is no difference between the master and slave units themselves.

[0101] S2. Check if a new APF has been added. If the host APF detects a new APF startup command, then it has been added; otherwise, it has not.

[0102] S3. If the relative position of the APF to be merged is known, in the APF nWith APF n-1 If n=1, then it is between APF1 and the load. The implementation method is as follows:

[0103] S31, The APF to be merged transmits the startup command.

[0104] S32. Each connected APF updates its compensation coefficient. Each connected APF updates its compensation coefficient based on the received startup command and known relative position information. n APF n+1 ...APF N Updated to APF n+1 APF n+2 ..., APF N+1 Then, the compensation coefficients can be calculated using the following formula:

[0105]

[0106] Where q represents APF q .

[0107] S33. Update compensation coefficients for the APF to be merged. The APF to be merged is updated to APF. n The compensation coefficient is: K dn = 1 / (N+2-n).

[0108] S4. If the relative position of the APF to be merged is unknown, the implementation method is as follows:

[0109] S41. The APF to be connected transmits the effective value of harmonic current harmonics from the near-side load. The APF to be connected detects the near-side load current and calculates the effective value i of the harmonic current. Ln-rms This data information is modulated and transmitted.

[0110] S42. Each connected APF updates its compensation coefficient. Each connected APF receives i Ln-rms The numerical information is compared with the locally detected effective value of harmonic current to obtain the relative position of the APF to be connected, and the compensation coefficient is updated accordingly. (Based on APF) m Received i Ln-rms For example, if the effective value of the locally detected harmonic current is i Lm-rms According to the following formula:

[0111]

[0112] By finding n, we can obtain the APF of the target APF. n With APF n-1 Between (n=1, then between APF1 and the load), therefore, APF1, APF2, ..., APF n-1 Unchanged, APFn APF n+1 ...APF N Updated to APF n+1 APF n+2 ..., APF N+1 To be incorporated into APF n Each connected APF updates its compensation coefficient according to this information using formula (11).

[0113] S43. The host APF transmits the compensation coefficients of the APFs to be merged into. The host APF, based on the relative position of the APFs to be merged into, according to K... dn =1 / (N+2-n) to calculate the compensation coefficient and perform modulation and transmission.

[0114] S44. Update the compensation coefficient of the APF to be merged. The APF to be merged is updated according to the received compensation coefficient information.

[0115] S5. Communication Detection and Fault Clearance. The master APF communicates with each slave APF every 1 hour. If there is no response after 3 queries with 1 second intervals, the APF is determined to be faulty, and a clearance command is sent to clear the APF. If a slave APF does not receive a query from the master within 1 hour, the master is determined to be faulty, and a clearance command is sent to clear the master, and the slave closest to the load side is selected as the new master.

[0116] S6. Each APF updates its compensation coefficient. The remaining APFs update their current relative position information according to the resection command, such as the resection APF. n Then APF n+1 APF n+2 ..., APF N Updated to APF n APF n+1 ...APF N-1 Then, the respective compensation coefficients can be calculated using the following formula:

[0117]

[0118] Where p represents APF p .

[0119] The following is used to verify that the embodiments of the present invention can achieve reliable information transmission while managing power quality, and the effectiveness of the current sharing control method.

[0120] APF multi-machine parallel system parameters (N=2):

[0121] Grid power supply U s =220V, equivalent inductance L s =0.05mH, inductive load L L=8mH, uncontrolled rectifier circuit DC side R=8Ω, L=2mH, C=700μF; inverter output filter inductor L out2 =L out1 =4mH, DC-side parallel support capacitor C dc2 =C dc1 =6000μF, DC side reference voltage V dc2 * =V dc1 * =340V. The APF closer to the load side is designated as APF1, and the one farther away is designated as APF2.

[0122] Information transmission system parameters:

[0123] Modulation parameters:

[0124] Baseband rate R b =100 b / s, carrier frequency f c =2.5kHz, PN sequence signal rate R c =2500 b / s, spreading factor k=25, initial value of PN sequence [1 0 0 1 1], generator polynomial of PN sequence "x 5 +x+1”, modulation sampling rate f s0 =50kHz. Pulse shaper parameters: Roll-off factor α = 0.7. Linear frequency modulation (LFM) waveform parameters (LFM sync head parameters): Start frequency f0 = 2200Hz, Stop frequency f1 = 2800Hz, LFM waveform duration T LFM =0.1s, duration of space T blank =0.01s, transmission sampling rate f s =50kHz.

[0125] Demodulation parameters:

[0126] Sampling rate f s =50kHz, local PN sequence parameters and modulation parameters are consistent.

[0127] APF1 is already in operation, but due to capacity limitations, it can only compensate for 80% of load harmonics and reactive current. Therefore, APF2 will be started for capacity expansion. Let Q... APF1 Q APF2 These represent the fundamental reactive power outputs of APF1 and APF2, respectively. Indicates circulation. Figure 8 , Figure 9The waveforms show the fundamental reactive power difference between the two APFs, the fundamental reactive power waveforms of the two APFs, and the circulating current waveforms, respectively, under the conditions of no current sharing control and with the current sharing control of this invention. The comparison reveals that without current sharing control, APF2 only compensates for the remaining 20% ​​of the load harmonics and reactive current, resulting in a relatively large circulating current (effective value of 5.5A). After current sharing control, the compensation currents of the two APFs are almost equal, and the circulating current is significantly reduced (effective value of 0.8A). Figure 10 The graphs show the grid current waveforms before and after load compensation using this embodiment. After compensation, the total harmonic distortion (THD) of the grid current decreased from 20.92% to 2.8%.

[0128] Figure 11 The waveform diagram shows the information demodulation process. As can be seen from the diagram, when simultaneously outputting the compensation current and transmitting the signal, the APF2 superimposes the DS-DPSK modulated data modulation wave onto the compensation command signal, affecting the grid voltage V. G Correspondingly, changes will occur, at which point APF1 can detect V. G The data information is then demodulated and recovered. The demodulated signal sequence is consistent with the source signal sequence, verifying the feasibility of the APF multi-machine parallel system based on integrated power / information transmission proposed in this embodiment of the invention.

[0129] Example 2

[0130] Embodiment 2 of the present invention provides a control system corresponding to Embodiment 1 above, including a memory, a processor and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method of Embodiment 1 above.

[0131] In some implementations, the memory may be high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device.

[0132] In other implementations, the processor can be any type of general-purpose processor, such as a central processing unit (CPU) or a digital signal processor (DSP), and there is no limitation here.

[0133] Example 3

[0134] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to Embodiment 1 above, on which a computer program / instructions are stored. When the computer program / instructions are executed by a processor, they implement the steps of the method of Embodiment 1 above.

[0135] A computer-readable storage medium can be a tangible device that holds and stores instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0136] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0137] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0138] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0139] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0140] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A current sharing control method for an APF multi-machine parallel system, characterized in that, Includes the following steps: S1. Configure one APF as the host; S2. Check if any new APF has been incorporated; S3. If a new APF is added, the compensation coefficients of each existing APF are updated according to different methods depending on whether the relative position of the new APF is known; the compensation coefficients of the newly added APF are updated; return to step S2. If no new APF is added, the master will query each slave APF sequentially at set intervals. If a slave does not respond to m queries at intervals of t1 seconds, the slave is determined to be faulty and disconnected. If the slave does not receive a query from the master within the set time, the master is determined to be faulty and disconnected, and the APF closest to the load side is selected as the new master. Each APF updates its current relative position information according to the disconnection command, then updates its own compensation coefficient, and returns to step S2. In step S1, when multiple APFs start simultaneously, the APF closest to the load side is designated as the master; otherwise, the APF that starts first is designated as the master. In step S3, the specific implementation process of updating the compensation coefficients of each connected APF according to different methods based on whether the relative position of the new APF is known includes: If the relative position of the APF to be merged is known, that is, the APF to be merged is in the APF n With APF n-1 When n=1, the APF to be incorporated is between APF1 and the load, then: The APF to be merged sends a startup command; Each connected APF receives the startup command. n APF n+1 ...APF N Updated to APF n+1 APF n+2 ..., APF N+1 The compensation coefficient K for each connected APF is calculated using the formula. dq : N is the total number of APFs; The APF to be merged is updated to APF n Using formula K dn =1 / (N+2-n) gives the compensation coefficient K. dn ; If the relative position of the APF to be merged is unknown, then: The APF to be connected detects the near-side load current and calculates the effective value of the harmonic current i. Ln-rms and send i Ln-rms Data information; Each connected APF receives i Ln-rms Numerical information, and the locally detected effective value of harmonic current i Lm-rms Compare according to the formula Obtain n, the APF to be merged into is in APF n With APF n-1 The relative positions of the APFs to be incorporated are obtained from the relationships between them; the compensation coefficient K of each already incorporated APF is then calculated using the formula. dq : ; The host APF uses formula K to determine the relative position of the APF to be merged into. dn =1 / (N+2-n) Calculate and send the compensation coefficient K to be merged into the slave APF. dn The compensation coefficient information will be received and updated by the APF.

2. The current sharing control method for an APF multi-machine parallel system according to claim 1, characterized in that, In step S3, the specific implementation process of the host querying each slave APF includes: 1) Source encoding is performed on the instruction information to obtain the information sequence. The instruction information is defined to consist of two parts: the first part is the 8-bit binary address of the APF; the second part is the start instruction, cut-off instruction, fault status code, compensation coefficient, and effective value of harmonic current. 2) Perform convolutional channel coding on the information sequence to obtain the encoded binary sequence {a}. i }, 1≤i≤N1, where a i N1 represents the i-th bit of the binary sequence, with a value of 0 or 1; N1 represents the length of the information sequence. 3) For {a i Differential encoding is performed to obtain the sequence to be sent, {d}. i },Right now Where a0 = 0, {d i The rate at which the sequence is converted into information is R. b The bipolar baseband signal d(t), i.e. ; =2d i -1,g T (t) is a value with an amplitude of 1 and a width of T. b =1 / R b The rectangular pulse, where t represents the time independent variable of the DS-DPSK waveform. T DS-DPSK The duration of the DS-DPSK waveform. Indicates the XOR operation; 4) Spread spectrum modulation is applied to d(t) to obtain the signal to be transmitted, b(t), i.e. Where c(t) is the information rate R. c The signal generated by the PN sequence signal generator ;{c i } is a PN sequence with values ​​of ±1, and p(t) is a sequence with an amplitude of 1 and a width of T. c =1 / R c A rectangular pulse, k=R c / R b Indicates the spreading factor; 5) Pulse shaping is performed on b(t) to obtain the signal to be modulated. , h(t) is the impulse response of the raised cosine roll-off filter; DS-DPSK waveform s(t) is generated: ;f c This is the cutoff frequency of the low-pass filter; 6) Obtain the final transmission signal : ; t1 is the time independent variable when calculating the linear frequency modulated wave, T LFM For the inserted linear frequency modulated wave s LFM The duration of (t1), f0 is the starting frequency of the linear frequency modulated wave, and Δf is the modulation frequency of the linear frequency modulated wave. t2 is the time variable of the blank window, T blank For blank window s blank The duration of (t2), t total T is the time independent variable of the final single-carrier signal. total T is the total duration of a single-carrier signal. total =T DS-DPSK +2T blank +2T LFM .

3. The current sharing control method for an APF multi-machine parallel system according to claim 2, characterized in that, The specific implementation process of the master querying each slave APF also includes: A) Acquire the grid voltage signal, filter out noise interference outside the signal frequency band using a bandpass filter, and obtain the signal r(t) to be demodulated; B) Combined with the length T of the LFM sync head LFM and the length T of the blank window blank The starting position τ0 of the acquired DS-DPSK waveform r(t) is: , τ max To make the linear frequency modulated signal s LFM (t) is the value of the independent variable when the correlation operation with the received signal takes the maximum correlation value; C) r m The despread data signal is obtained by multiplying the local PN sequence signal c(t) (which is the same as that of the signal generation module) by the signal generation module. : ; D) will Delayed by one baseband signal period T b , and then with Multiplication achieves difference decomposition and tuning: ; =2a i -1, ; E) The above output results Through a cutoff frequency at f c and 2f c A low-pass filter is used to filter out the second harmonic signal component, resulting in a preliminary demodulated signal. F) The preliminary demodulated signal is sampled and decided, with the optimal sampling point located in the middle of the symbol. Sampling is then performed every symbol period. Sampling points with a decision value greater than 0 are determined as "0", and sampling points with a decision value less than 0 are determined as "1", thus obtaining the original information sequence {a}. i } 4. The current sharing control method for an APF multi-machine parallel system according to claim 3, characterized in that, Also includes: G) for {a i Perform maximum a posteriori (MAP) decoding on the convolutional code and select the bit with the maximum a posteriori probability as the received bit. H) According to the rules in the information modulation process, the received bits are decoded. The first 8 received bits are decoded into the APF address, and the latter part of the received bits are decoded into the corresponding start command, switching command, fault status, compensation coefficient, and effective value of harmonic current.

5. The current sharing control method for an APF multi-machine parallel system according to claim 1, characterized in that, In step S3, when no new APF is incorporated, the compensation coefficient K of each APF is... dp The updated formula is: .

6. A current sharing control system for an APF multi-machine parallel system, characterized in that, include: One or more processors; A memory having stored one or more programs thereon, which, when executed by the one or more processors, cause the one or more processors to perform the steps of the method according to any one of claims 1 to 5.

7. A computer-readable storage medium, characterized in that, It stores a computer program that, when executed by a processor, implements the steps of the method as described in any one of claims 1 to 5.

Images