APF Multi-Machine Parallel System Control Method and System

Abstract

This invention discloses a control method and system for a multi-APF parallel system, applicable to systems with N APFs operating in parallel. It includes two levels of control units: a central controller as the primary control unit and each APF controller as a secondary control unit. The primary control unit calculates the feedforward coefficient based on the rated compensation capacity of each APF and transmits it to the secondary control unit. The secondary control unit detects harmonic currents through current sensors connected to the grid side and the load side, and then outputs the compensation current. By subtracting the output current feedback signal from the reference current signal, the reference current is reduced proportionally to the output current, achieving automatic distribution of the output current of each APF according to its rated capacity. This invention can also improve the system's compensation accuracy based on the feedforward coefficient transmitted by the primary control unit. This invention improves the flexibility, scalability, and reliability of the multi-APF parallel system. When the central controller fails or equipment communication fails, each APF can still operate independently and automatically distribute the compensation current.

Description

Technical Field

[0001] This invention relates to the technology of multiple active power filter (APF) systems in parallel, and in particular to a control method and system for a multi-machine parallel APF system. Background Technology

[0002] With the continuous increase in power system load and the widespread application of power electronic equipment, power quality problems are becoming increasingly severe, especially harmonic pollution and reactive power fluctuations. In low-voltage, high-current applications, traditional single active power filters (APFs) face limitations in capacity and stability, making it difficult to meet the power quality management needs of modern power grids. Therefore, the technology of parallel operation of multiple APFs has emerged. By operating multiple APFs in parallel, the system's compensation capability and stability can be significantly improved, effectively responding to dynamic load changes and meeting the power quality improvement needs of large-scale power systems. However, parallel operation of multiple units requires an efficient control strategy to coordinate the operation of each unit and achieve reasonable load distribution. Therefore, researching a highly reliable multi-unit coordinated control strategy has significant practical implications.

[0003] In systems with communication lines, most solutions achieve harmonic current distribution through communication between active power filters or centralized control via a host computer. Examples include "Dynamic Coordination Control Method for High-Power APF Parallel Harmonic Compensation System" (Publication No.: CN105356470A), "Power Quality Comprehensive Management Device Based on Multi-Machine Parallel Sequential Control" (Publication No.: CN110380433A), and "An Optimized Operation Control Method for Multi-Machine Parallel Active Power Filters" (Publication No.: CN104882885A). However, this control method has weak scalability and stability; if the main controller or communication fails, the entire system will struggle to operate normally. Furthermore, there are master-slave control and distributed control methods, all of which rely heavily on communication between devices. If communication fails, harmonic current distribution cannot be achieved. To address this, the patent application "Parallel Control Method and System for Multiple Parallel Power Quality Management Devices" (Publication No.: CN110266023A) proposes a hardware analog bus solution, allowing the system to continue operating normally even if the central processing unit is offline or hardware communication malfunctions. However, this solution is essentially equivalent to adding another set of communication equipment, requiring an additional loop circuit and corresponding circuit design for each device controller, which increases system cost and reduces scalability.

[0004] In the no-communication-line mode, each APF only compensates for the remaining harmonics not fully compensated by the previous one. This control method allows each APF to operate independently, thereby improving the system's reliability and redundancy. However, this method cannot achieve harmonic current distribution. Especially the APFs closer to the load side are prone to excessive aging due to prolonged full-load operation, and the overall dynamic response capability of the system is also poor. Patent application "APF Multi-Machine Parallel System Current Sharing Control Method, System and Storage Medium" (Publication No.: CN116960992A) adopts a method of synchronous transmission of power information, which does not require additional communication line connections. It achieves uniform distribution of harmonic current through communication between devices via power lines, and the system adopts master-slave control, resulting in high reliability. However, the system response speed is slow due to limitations in communication rate. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a control method and system for an APF multi-machine parallel system, which addresses the shortcomings of the existing technology and solves the problem that the system cannot operate normally or cannot achieve harmonic current distribution when the main controller or communication fails in the control strategy with communication line; and the problem that the system response speed is slow in the control strategy without communication line.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a control method for an APF multi-machine parallel system, wherein the APF multi-machine parallel system includes N APFs, the N APFs are connected in parallel to the power grid, each APF includes a DC-side capacitor, an H-bridge inverter, and an output filter inductor connected in sequence; the H-bridge inverter is connected to an APF controller; the APF controller in each APF is connected to a central controller; N≥2; including the following steps:

[0007] Determine the APF with the largest rated capacity among N APFs, and let the rated capacity of this APC be I. max Its feedback coefficient is D max , 0≤D max ≤1; Set the feedback coefficient of other APFs to D. n The subscript n represents the nth APF, 1≤n≤N;

[0008] Extract grid connection point voltage V PCC Phase angle θ, grid-side current i s dq axis harmonic components i sdf i sqf Load side current i L dq axis harmonic components i Ldh i Lqh The output current i on the AC side of the nth APF cn dq axis harmonic components i cndh i cnqh ;

[0009] When the central controller is working normally and communication is normal, the feedforward coefficient K is transmitted by the central controller. ff When the central controller or communication fails, the feedforward coefficient K is given. ff =0;

[0010] Using the feedback coefficient of APF and the grid-side current i s dq axis harmonic components, load-side current i L The dq-axis harmonic components, the AC side output current i of the nth APF cn dq-axis harmonic component calculation reference dq-axis harmonic component i cndh_ref i cnqh_ref :

[0011] DC side capacitor voltage v dcn and DC side voltage reference value v dcn_ref After comparison, the difference is passed through a PI controller to obtain the fundamental active component i. cndf_ref ;

[0012] Using the fundamental active component i cndf_ref The reactive current component i to be compensated is obtained from the feedforward coefficient and the feedback coefficient of the nth APF. cnqf_ref ;

[0013] Calculate the dq-axis reference component i of the output current cnd_ref i cnq_ref ; the reference component i of the output current dq axis cnd_ref i cnq_ref The current signal in the stationary coordinate system is obtained after inverse Park transformation. After passing through a current limiting circuit, the output current reference signal i is obtained. cn_ref ;

[0014] will i cn_ref with i cn After comparison, the difference is processed by the PR controller and then the grid connection point voltage V is applied. PCC Feedforward to obtain the inverter modulation wave signal, and then use sinusoidal pulse width modulation to obtain the inverter switching trigger signal to drive the inverter to work.

[0015] The harmonic current distribution of the present invention is determined by the output current feedback coefficient set by each APF, without relying on communication. Each APF has the ability to operate independently. Therefore, the problems of the system failing to operate normally or failing to achieve harmonic current distribution due to failure of the main controller or communication, as well as the slow system response speed, which are present in previous control strategies, are not present.

[0016] The feedback coefficient D of the nth APF n The calculation formula is: Among them, I cn This represents the rated compensation capacity of the nth APF.

[0017] Extract grid connection point voltage V PCC Phase angle θ, grid-side current i s dq axis harmonic components, load-side current i L The dq-axis harmonic components and the AC output current i of the nth APF cn The specific implementation process of the dq-axis harmonic components includes: converting i s The dq-axis components i in the fundamental frequency rotating coordinate system are obtained through the Park transformation. sd i sq The fundamental component i of the dq axis is extracted using a moving average filter. sdf i sqf Furthermore, the dq-axis harmonic components i are obtained. sdh＝ i sd -i sdf i sqh＝ i sq -i sqf Similarly, i L dq axis harmonic components i Ldh i Lqh and i cn dq axis harmonic components i cndh i cnqh .

[0018] The transfer function of the moving average filter is: Where T w Let s be the duration of the sliding window, where s is a complex variable.

[0019] Feedforward coefficient K ff The calculation formula is: I cn This represents the rated compensation capacity of the nth APF.

[0020] dq axis harmonic components i cndh_ref i cnqh_ref The calculation formula is:

[0021]

[0022] Where K is the harmonic current control gain.

[0023] The reactive current component i to be compensated cnqf_ref The calculation formula is: i cnqf_ref =Ki sqf -D n i cnqf +K ff i Lqf K represents the harmonic current control gain.

[0024] Output current dq axis reference component i cnd_ref i cnq_ref The calculation formula is:

[0025]

[0026] Output current reference signal i cn_ref The calculation formula is: Among them, i cn_ref1 =i cnd_ref sinθ+i cnq_ref cosθ.

[0027] As an inventive concept, the present invention also provides an APF multi-machine parallel system control system, including a memory, a processor, and a computer program stored in the memory; the processor executes the computer program to implement the steps of the above method.

[0028] As an inventive concept, the present invention also provides a computer-readable storage medium having a computer program / instructions stored thereon; when the computer program / instructions are executed by a processor, they implement the steps of the above-described method.

[0029] Compared with existing technologies, the beneficial effects of this invention are as follows: By setting the output current feedback coefficient of each APF, this invention can automatically distribute the output current of each APF according to its rated capacity ratio; the load current feedforward coefficient transmitted by the primary control unit can further improve the overall compensation accuracy of the system; when one APF fails, its secondary control unit controls it to exit operation, and the remaining APFs can respond quickly and automatically distribute the compensation current. Compared with existing control methods, the harmonic current distribution of this invention is determined by the output current feedback coefficient set for each APF, without relying on communication. Each APF has the ability to operate independently, thus avoiding the problems of system failure or inability to achieve harmonic current distribution due to main controller or communication failures, as well as the problem of slow system response speed in previous control strategies; this invention does not require additional equipment and circuits, resulting in lower cost and stronger scalability. The feedforward coefficient information transmitted between the primary and secondary control units in this invention only serves to improve the system compensation accuracy. Even if the feedforward coefficient information cannot be transmitted due to a failure of the primary control unit or communication, the automatic distribution of harmonic current can still be guaranteed, without significantly affecting the normal operation of the system. Attached Figure Description

[0030] Figure 1 This invention proposes an APF multi-machine parallel system and its hierarchical coordinated control method;

[0031] Figure 2This is a block diagram illustrating the principle of harmonic current detection.

[0032] Figure 3 This is a flowchart of the hierarchical coordinated control method for a two-level control unit proposed in this invention.

[0033] Figure 4 The grid current waveform and its FFT analysis results before the APF multi-machine parallel system is put into operation;

[0034] Figure 5 The output current waveforms, grid-side current waveforms, and FFT analysis results of each APF under operating condition 1; (a) all three APFs are operating normally, (b) the primary control unit or communication fails, and (c) APF2 fails and exits.

[0035] Figure 6 The output current waveforms and grid-side current waveforms of each APF under operating condition 2 are as follows: (a) all three APFs are operating normally; (b) the primary control unit or communication fails; (c) APF2 fails and exits. Detailed Implementation

[0036] 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.

[0037] Example 1

[0038] like Figure 1 As shown, the APF multi-machine parallel system of this embodiment includes N (N≥2) single-phase APFs connected in parallel to the power grid, and each APF includes a DC-side capacitor C. n H-bridge inverter composed of MOSFETs, and output filter inductor L n The system includes an APF controller; it comprises two levels of control units, with the central controller being the primary control unit and each APF controller being the secondary control unit; a current sensor is installed on both the grid side and the load side to detect the current signal and transmit it to each secondary control unit. Figure 1 In this context, the 1st, ..., nth, ..., Nth APFs are denoted as APF1, ..., APF2, ... n ..., APF N u s L is the grid voltage. s For equivalent inductance; i s i L For grid-side current and load-side current; icn v dcn V PCC The output compensation current, DC side capacitor voltage, and grid connection point voltage of the nth APF (1≤n≤N) are provided; harmonics and reactive current in the power grid are provided by inductive loads and uncontrolled rectifier circuits.

[0039] The primary control unit actively communicates with each secondary control unit to obtain the rated compensation capacity of each APF and calculates the feedforward coefficient, which is then transmitted to all secondary control units.

[0040] The secondary control unit, based on the transmitted grid-side current and load-side current signals, as well as the locally detected DC-side capacitor voltage, AC-side output current, and grid connection point voltage signals, and combined with the feedforward coefficient transmitted by the primary control unit, adopts a hierarchical coordinated control method to obtain the output current reference signal, and generates a switching signal based on the output current reference signal to drive the inverter to work.

[0041] like Figure 3 As shown, the hierarchical coordinated control method adopted by the secondary control unit in this embodiment of the invention includes the following steps:

[0042] S1. Determine the APF with the largest rated capacity among the N APFs; its rated capacity is I. max Set its feedback coefficient D max , 0≤D max ≤1;

[0043] S2. Set the feedback coefficients D for other APFs. n The subscript n represents the nth APF, 1≤n≤N, and the feedback coefficient D n The calculation formula is:

[0044]

[0045] Among them I cn This represents the rated compensation capacity of the nth APF;

[0046] S3. Extract the grid connection point voltage V using a digital phase-locked loop (PLL). PCC The phase angle θ provides phase information for the Park transform and inverse transform;

[0047] S4. Harmonic current detection, extracting the grid-side current i s Load side current i L and the AC output current i of the nth APF cn The dq-axis harmonic components. The principle block diagram is as follows: Figure 2 As shown, i x (x = s, L, cn) Delayed by 1 / 4 of a fundamental period, we obtain Then, using the single-phase Park transformation formula:

[0048]

[0049] Obtain the dq axis components i xd i xq The dq-axis fundamental component i is extracted using a moving average filter (MAF). xdf i xqf Furthermore, the dq-axis harmonic components i are obtained. xdh＝ i xd -i xdf i xqh＝ i xq -i xqf x = s, L, cn;

[0050] The transfer function of MAF is:

[0051]

[0052] Where T w The duration of the sliding window;

[0053] S5, Harmonic Current Distribution Control. When the primary control unit and communication are working normally, the feedforward coefficient K is transmitted by the primary control unit. ff When the primary control unit or communication fails, K cannot be received. ff Given K directly ff =0. The first-level control unit calculates the feedforward coefficient K. ff The formula is:

[0054]

[0055] The reference dq axis harmonic component i is calculated using the formula. cndh_ref i cnqh_ref :

[0056]

[0057] Where K is the harmonic current control gain; D n Let be the feedback coefficient of the nth APF;

[0058] S6, DC-side voltage regulation control. This involves controlling the extracted DC-side capacitor voltage v. dcn and DC side voltage reference value v dcn_ref After comparison, the difference is processed by a PI controller to obtain the fundamental active component i. cndf_ref ;

[0059] S7. Reactive current control. The reactive current component i to be compensated is obtained using the formula. cnqf_ref :

[0060] i cnqf_ref=Ki sqf -D n i cnqf +K ff i Lqf (6)

[0061] S8, inverse Park transform, and current limiting. Calculate the dq-axis reference component i of the output current using the formula. cnd_ref i cnq_ref :

[0062]

[0063] Then, the current signal i in the stationary coordinate system is obtained by inverse Park transformation. cn_ref1 The formula for the single-phase inverse transformation is:

[0064] i cn_ref1 =i cnd_ref sinθ+i cnq_ref cosθ; (8)

[0065] After a current limiting circuit is used to ensure that the output current does not exceed its own capacity, the output current reference signal i is obtained. cn_ref The expression for the current limiting circuit is:

[0066]

[0067] S9, Current Tracking Control. (The last part, "i", appears to be a typo and doesn't translate directly. cn_ref with i cn After comparison, the difference is processed by the PR controller and then the grid connection point voltage V is applied. PCC The inverter modulation signal is obtained through feedforward. The PR controller resonant points are at the main harmonic frequencies, namely the 3rd, 5th, 7th, and 9th harmonics, and its transfer function is:

[0068]

[0069] Where, k p k is the proportionality coefficient. r ω is the resonance coefficient. c ω is the cutoff angular frequency. s This is the system angular frequency.

[0070] Finally, the inverter modulation wave signal is obtained by sinusoidal pulse width modulation (SPWM) to trigger the inverter switch and drive the inverter to work.

[0071] S10. Fault Monitoring. Real-time monitoring of APF operating status information; in the event of a short circuit, damage to switching devices, or other faults, the connection to the power grid is quickly disconnected, and the system is taken out of service.

[0072] The following is used to verify that the embodiments of the present invention can automatically distribute the output current of each APF according to its rated capacity ratio. When the primary control unit and communication are normal, the system has high compensation accuracy; when the primary control unit and communication fail, the system can still continue to operate; after one APF fails and exits, the remaining APFs can respond quickly and automatically distribute the compensation current.

[0073] System parameters:

[0074] Grid voltage u s =220V, system angular frequency ω s =100π, equivalent inductance L s =0.1mH;

[0075] Reactive load parameters:

[0076] resistor R r =1Ω, inductance L r =10mH;

[0077] Nonlinear load parameters:

[0078] Two identical single-phase bridge rectifier circuits are connected in parallel, with DC-side filter inductance L = 2mH, filter capacitor C = 700μF, and load resistance R = 5Ω;

[0079] APF multi-machine parameters (N=3):

[0080] The inverter's AC side output filter inductor L1 = L2 = L3 = 2.5mH, and the DC side capacitor...

[0081] C1 = C2 = C3 = 6000μF, DC side reference voltage v dc1_ref =v dc2_ref =v dc3_ref =600V;

[0082] Control parameters:

[0083] Feedback coefficient D of maximum capacity APF max =0.1, harmonic current control gain K=1.2, sliding window time T of MAF w =0.02s, PR controller parameter k p =0.16, k r =1.6, ω c =0.4π;

[0084] When the APF parallel system is not in operation, the grid-side current waveform and FFT analysis results are as follows: Figure 4 As shown, the total harmonic distortion rate is as high as 42.04%, mainly due to the 3rd, 5th, 7th and 9th harmonics.

[0085] Operating Condition 1: When the rated capacity of the three APFs is the same, I1 = I2 = I3 = 100A; then I max =100A, according to formula (1), set D1=D2=D3=D max =0.1;

[0086] If the primary control unit communicates normally, K is calculated according to formula (4). ff =11 / 30, such as Figure 5 As shown in (a), the output current of the three APFs is exactly the same, and the grid-side current THD decreases from 42.04% to 1.15%, which shows a good treatment effect.

[0087] If the primary control unit or communication fails, the secondary unit directly sets K. ff =0, such as Figure 5 In (b), the output current of the three APFs remains exactly the same, and the grid-side current THD decreases from 42.04% to 7.18%, resulting in a decrease in system compensation accuracy. However, each APF can still automatically distribute the compensation current according to its rated capacity.

[0088] If APF2 shuts down due to a fault, the other APFs continue to operate normally. Figure 5 As shown in (c), the output currents of APF1 and APF3 remain consistent, and the grid-side current THD decreases from 42.04% to 1.23%, indicating a fast system response and short fault transition time.

[0089] Operating Condition 2: When the rated capacities of the three APFs are not the same, I1 = I2 = 120A, I3 = 60A; then I max =120A, according to formula (1), set D1=D2=D max =0.1, D3=1.2;

[0090] If the primary control unit communicates normally, K is calculated according to formula (4). ff =11 / 25, as Figure 6 As shown in (a), the output currents of APF1 and APF2 are exactly the same, while the output current of APF3 is half that of APF1. The grid-side current THD decreased from 42.04% to 1.07%, indicating a good treatment effect.

[0091] If the primary control unit or communication fails, the secondary unit directly sets K. ff =0, such as Figure 6 In (b), APF1 and APF2 have the same output current, while APF3 has half the output current of APF1. The grid-side current THD drops from 42.04% to 8.32%, and the system compensation accuracy decreases. However, each APF can still automatically distribute the compensation current according to the rated capacity ratio.

[0092] If APF2 shuts down due to a fault, the other APFs continue to operate normally. Figure 6 As shown in (c), APF1 and APF2 have the same output current, while the output current of APF3 is half that of APF1. The grid-side current THD drops from 42.04% to 1.20%, indicating a fast system response and short fault transition time.

[0093] Example 2

[0094] 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.

[0095] 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.

[0096] 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.

[0097] Example 3

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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 control method for an APF multi-machine parallel system, wherein the APF multi-machine parallel system comprises N APFs connected in parallel to the power grid, each APF comprising a DC-side capacitor, an H-bridge inverter, and an output filter inductor connected in sequence; the H-bridge inverter is connected to an APF controller; the APF controller in each APF is connected to a central controller; N≥2; characterized in that, Includes the following steps: Determine the APF with the largest rated capacity among N APFs, and let the rated capacity of this APC be I. max Its feedback coefficient is D max , 0≤D max ≤1; Set the feedback coefficient of other APFs to D. n The subscript n represents the nth APF, 1≤n≤N; Extract grid connection point voltage V PCC Phase angle θ, grid-side current i s dq axis harmonic components i sdf i sqf Load side current i L dq axis harmonic components i Ldh i Lqh The output current i on the AC side of the nth APF cn dq axis harmonic components i cndh i cnqh ; When the central controller is working normally and communication is normal, the feedforward coefficient K is transmitted by the central controller. ff When the central controller or communication fails, the feedforward coefficient K is given. ff =0; Using the feedback coefficient of APF and the grid-side current i s dq axis harmonic components, load-side current i L The dq-axis harmonic components, the AC side output current i of the nth APF cn dq-axis harmonic component calculation reference dq-axis harmonic component i cndh_ref i cnqh_ref : DC side capacitor voltage v dcn and DC side voltage reference value v dcn_ref After comparison, the difference is passed through a PI controller to obtain the fundamental active component i. cndf_ref ; Using the fundamental active component i cndf_ref The reactive current component i to be compensated is obtained from the feedforward coefficient and the feedback coefficient of the nth APF. cnqf_ref ; Calculate the dq-axis reference component i of the output current cnd_ref i cnq_ref ; The dq-axis reference component of the output current i cnd_ref i cnq_ref The current signal in the stationary coordinate system is obtained after inverse Park transformation. After passing through a current limiting circuit, the output current reference signal i is obtained. cn_ref ; will i cn_ref with i cn After comparison, the difference is processed by the PR controller and then the grid connection point voltage V is applied. PCC Feedforward to obtain the inverter modulation wave signal, and then use sinusoidal pulse width modulation to obtain the inverter switching trigger signal to drive the inverter to work.

2. The APF multi-machine parallel system control method according to claim 1, characterized in that, The feedback coefficient D of the nth APF n The calculation formula is: Among them, I cn This represents the rated compensation capacity of the nth APF.

3. The APF multi-machine parallel system control method according to claim 1, characterized in that, Extract grid connection point voltage V PCC Phase angle θ, grid-side current i s dq axis harmonic components, load-side current i L The dq-axis harmonic components and the AC output current i of the nth APF cn The specific implementation process of the dq-axis harmonic components includes: converting i s The dq-axis components i in the fundamental frequency rotating coordinate system are obtained through the Park transformation. sd i sq The fundamental component i of the dq axis is extracted using a moving average filter. sdf i sqf Furthermore, the dq-axis harmonic components i are obtained. sdh =i sd -i sdf i sqh =i sq -i sqf Similarly, i L dq axis harmonic components i Ldh i Lqh and i cn dq axis harmonic components i cndh i cnqh .

4. The APF multi-machine parallel system control method according to claim 3, characterized in that, The transfer function of the moving average filter is: Where T w Let s be the duration of the sliding window, where s is a complex variable.

5. The APF multi-machine parallel system control method according to claim 1, characterized in that, Feedforward coefficient K ff The calculation formula is: I cn This represents the rated compensation capacity of the nth APF.

6. The APF multi-machine parallel system control method according to claim 3, characterized in that, dq axis harmonic components i cndh_ref i cnqh_ref The calculation formula is: Where K is the harmonic current control gain.

7. The APF multi-machine parallel system control method according to claim 3, characterized in that, The reactive current component i to be compensated cnqf_ref The calculation formula is: i cnqf_ref =Ki sqf -D n i cnqf +K ff i Lqf K represents the harmonic current control gain.

8. The APF multi-machine parallel system control method according to claim 3, characterized in that, Output current dq axis reference component i cnd_ref i cnq_ref The calculation formula is:

9. The APF multi-machine parallel system control method according to claim 1, characterized in that, Output current reference signal i cn_ref The calculation formula is: Among them, i cn_ref1 =i cnd_ref sinθ+i cnq_ref cosθ.

10. A control system for an APF multi-machine parallel system, comprising a memory, a processor, and a computer program stored in the memory; characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 9.

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