APF multi-machine parallel system control method and system

Abstract

The invention discloses a method and a system for controlling an APF (active power filter) multi-machine parallel system, which are suitable for a system in which N APFs run in parallel. The system comprises two stages of control units, a central controller is a first-stage control unit, and each APF controller is a second-stage control unit. The first-stage control unit calculates a feed-forward coefficient according to the rated compensation capacity of each APF and transmits the feed-forward coefficient to the second-stage control unit; the second-stage control unit detects harmonic current through current sensors connected to the network side and the load side and then outputs compensation current. The output current feedback signal is subtracted from the reference current signal, so that the reference current and the output current are proportionally reduced, and the output current of each APF is automatically distributed according to the rated capacity proportion; the compensation precision of the system can be improved according to the feed-forward coefficient transmitted by the first-stage control unit. According to the method, the flexibility, the expansibility and the reliability of the APF multi-machine parallel system can be improved, and when a central controller fails or equipment communication fails, each APF can still operate independently, and compensation current is automatically distributed.

Description

Technical Field

[0001] The invention relates to an active power filter multi-machine parallel connection technology, in particular to an APF multi-machine parallel connection system control method and system. Background Art

[0002] With the continuous increase of power system load and the widespread application of power electronic equipment, power quality issues are becoming increasingly severe, especially harmonic pollution and reactive power fluctuations. In low-voltage and high-current applications, the traditional single active power filter (APF) faces capacity and stability limitations, and it is difficult to meet the needs of modern power grids for power quality management. Therefore, APF multi-machine parallel operation technology came into being. By working in parallel with multiple APFs, the compensation capacity and stability of the system can be significantly improved, dynamic load changes can be effectively responded to, and the needs of large-scale power systems for improving power quality can be met. However, multi-machine parallel operation requires an efficient control strategy to coordinate the work of each unit and achieve reasonable load distribution. Therefore, it is of great practical significance to study a high-reliability multi-machine coordinated control strategy.

[0003] In the case of communication lines, most schemes achieve the purpose of harmonic current distribution by communicating between active power filters or setting up a host computer for centralized control, such as "Dynamic coordination control method for high-power APF parallel harmonic compensation system" (publication number: CN105356470A), "Power quality comprehensive management device based on multi-machine parallel sequence control" (publication number: CN110380433A), "A method for optimizing operation of multi-machine parallel active power filter" (publication number: CN104882885A). This control method has weak scalability and stability. Once the main controller or communication fails, the entire system will be difficult to operate normally. In addition, there are control methods such as master-slave control and distributed control. These control methods are too dependent on communication between devices. If the communication fails, harmonic current distribution cannot be achieved. For this reason, the patent application "Parallel control method and system for multiple parallel power quality management devices" (publication number: CN110266023A) proposes a hardware simulation bus solution. Even if the central processor is offline or the hardware communication is abnormal, the system can still work normally. However, this solution is essentially equivalent to adding another set of communication equipment, which requires an additional set of loop circuits, and each device controller also needs to add corresponding circuit designs, resulting in increased system costs and reduced scalability.

[0004] In the mode without communication lines, each APF only compensates for the remaining harmonics that were not fully compensated by the previous one. This control method enables each APF to operate independently, thereby improving the reliability and redundancy of the system. However, this method cannot achieve harmonic current distribution. In particular, the APF close to the load side is prone to excessive aging due to being in full-load operation for a long time. At the same time, the overall dynamic response capability of the system is also poor. The patent application "APF multi-machine parallel system current control method, system and storage medium" (publication number: CN116960992A) adopts a method for synchronous transmission of electric energy information. It does not require additional communication lines to connect, and communicates between devices through power lines, realizing uniform distribution of harmonic currents. The system adopts master-slave control with high reliability, but is limited by the communication rate and the system response speed is slow. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an APF multi-machine parallel system control method and system in view of the deficiencies in the prior art, so as to solve the problem that in a control strategy with a communication line, when the main controller or the communication fails, the system cannot operate normally or cannot achieve harmonic current distribution; and the problem that in a control strategy without a communication line, the system has a slow response speed.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a control method for an APF multi-machine parallel system, 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; comprising the following steps:

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

[0008] Extract the grid voltage V PCC The phase angle θ and grid-side current i s The dq-axis harmonic component i sdf 、i sqf , load side current i L The dq-axis harmonic component i Ldh ,i Lqh 、The AC output current i of the nth APF cn The dq-axis harmonic component i cndh ,i cnqh ;

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

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

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

[0012] Using the fundamental wave active component i cndf_ref , feedforward coefficient, feedback coefficient of the nth APF to obtain the reactive current component i to be compensated cnqf_ref ;

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

[0014] will i cn_ref with i cn After comparison, the difference passes through the PR controller and then adds the grid voltage V PCC Feedforward to obtain the inverter modulation wave signal, and obtain the inverter switch trigger signal by sinusoidal pulse width modulation to drive the inverter to work.

[0015] The harmonic current distribution of the present 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. Therefore, there is no problem in previous control strategies that the system cannot operate normally or cannot achieve harmonic current distribution due to failure of the main controller or communication, and there is no problem of slow system response speed.

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

[0017] Extract the grid voltage V PCC The phase angle θ and grid-side current i s The dq-axis harmonic components and 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: s Through Park transformation, we can get the dq axis component i in the fundamental frequency rotating coordinate system. sd 、i sq , use the sliding average filter to extract the dq axis fundamental component i sdf 、i sqf , and further obtain the dq-axis harmonic component i sdh＝ i sd -i sdf 、i sqh＝ i sq -i sqf , similarly L The dq-axis harmonic component i Ldh ,i Lqh and i cn The dq-axis harmonic component i cndh ,i cnqh .

[0018] The transfer function of the sliding average filter is: Where T w is the sliding window time length, and s is a complex variable.

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

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

[0021]

[0022] Wherein, K is the harmonic current control gain.

[0023] Reactive current component to be compensated i cnqf_ref The calculation formula is: cnqf_ref =Ki sqf -D n i cnqf +K ff i Lqf ; K is 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 / instruction stored thereon; the computer program / instruction implements the steps of the above method when executed by a processor.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: by setting the output current feedback coefficient of each APF, the output current of each APF can be automatically distributed according to the proportion of their respective rated capacities; the load current feedforward coefficient transmitted by the primary control unit can further improve the overall compensation accuracy of the system; when a certain APF fails, its secondary control unit controls the exit from operation, and the remaining APFs can respond quickly and automatically distribute the compensation current. Compared with the existing control method, the harmonic current distribution of the present invention is determined by the output current feedback coefficient set by each APF, without relying on communication, and each APF has the ability to operate independently, so there is no problem in the previous control strategy that the system cannot operate normally or cannot achieve harmonic current distribution due to failure of the main controller or communication, and the problem of slow system response speed; the present invention does not require additional equipment and circuits, and has lower cost and stronger scalability. In the present invention, the feedforward coefficient information transmitted by the primary control unit and the secondary control unit in mutual communication only serves to improve the compensation accuracy of the system. Even if the feedforward coefficient information cannot be transmitted due to failure of the primary control unit and communication, the automatic distribution of harmonic current can be guaranteed, and the normal operation of the system will not be greatly affected. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 An APF multi-machine parallel system and a hierarchical coordinated control method thereof proposed by the present invention;

[0031] Figure 2This is the principle block diagram of harmonic current detection;

[0032] Figure 3 It is a flowchart of the hierarchical coordinated control method of the two-level control unit proposed by the present invention;

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

[0034] Figure 5 The output current waveforms of each APF, the grid-side current waveforms and their FFT analysis results under working condition 1; (a) normal operation of the three APFs, (b) primary control unit or communication failure, (c) APF2 failure exit;

[0035] Figure 6 The output current waveforms of each APF, the grid-side current waveforms and their FFT analysis results under the second working condition; (a) the three APFs are operating normally, (b) the first-level control unit or communication failure, and (c) APF2 fault exits. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work 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 the embodiment of the present invention 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 MOSFET, output filter inductor L n And APF controller; the system includes two levels of control units, the central controller is the first-level control unit, and each APF controller is the second-level control unit; a current sensor is installed on the grid side and the load side to detect the current signal and transmit it to each second-level control unit. Figure 1 In the example, the 1st, ..., nth, ..., and Nth APFs are denoted as APF1, ..., APF n , …, APF N ,u s is the grid voltage, L s is the equivalent inductance; i s 、i L is the grid-side current and load-side current; icn 、v dcn 、V PCC It is the output compensation current, DC side capacitor voltage, and grid connection point voltage of the nth APF (1≤n≤N); the harmonics and reactive current in the grid are provided by the inductive load and uncontrolled rectifier circuit.

[0039] The first-level control unit actively communicates with each second-level control unit to obtain the rated compensation capacity of each APF, and calculates the feedforward coefficient and transmits it to all second-level control units.

[0040] The secondary control unit adopts a hierarchical coordinated control method based on the transmitted grid-side current, load-side current signals, and locally detected DC-side capacitor voltage, AC-side output current and grid-connected point voltage signals, combined with the feedforward coefficient transmitted by the primary control unit, 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 of the embodiment of the present invention includes the following steps:

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

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

[0044]

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

[0046] S3, use digital phase-locked loop (PLL) to extract the grid voltage V PCC The phase angle θ provides phase information for Park transform and inverse transform;

[0047] S4, harmonic current detection, respectively extract 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) delays 1 / 4 fundamental period, and we get Then use the single-phase Park transformation formula:

[0048]

[0049] Get the dq axis component i xd 、i xq , extract the dq axis fundamental component i through the moving average filter (MAF) xdf 、i xqf , and further obtain the dq-axis harmonic component i 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 is the sliding window time length;

[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 , directly given K 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 is the feedback coefficient of the nth APF;

[0058] S6, DC side voltage regulation control. The extracted DC side capacitor voltage v dcn and DC voltage reference value v dcn_ref After comparison, the difference is passed through the 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 transformation and current limitation. The output current dq axis reference component i is calculated using the formula cnd_ref ,i cnq_ref :

[0062]

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

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

[0065] After the current limiting link, ensure that the output current does not exceed its own capacity, and obtain the output current reference signal i cn_ref The current limiting link expression is:

[0066]

[0067] S9, current tracking control. cn_ref with i cn After comparison, the difference passes through the PR controller and then adds the grid voltage V PCC The inverter modulation wave signal is obtained by feedforward. The resonance point of the PR controller is at the main harmonic frequency, that is, the 3rd, 5th, 7th, and 9th, and its transfer function is:

[0068]

[0069] Among them, k p is the proportionality coefficient, k r is the resonance coefficient, ω c is the cut-off angular frequency, ω s is the system angular frequency.

[0070] Finally, the inverter modulation wave signal is modulated by sinusoidal pulse width modulation (SPWM) to obtain the inverter switch trigger signal to drive the inverter to work;

[0071] S10, Fault monitoring. Real-time monitoring of APF operation status information. When a short circuit, switch component damage or other faults occur, the connection with the grid is quickly cut off and the operation is stopped;

[0072] The following is used to verify that the embodiment of the present invention can achieve automatic distribution of the output current of each APF according to the rated capacity ratio. When the primary control unit and communication are normal, the system has a high compensation accuracy; when the primary control unit and communication fail, the system can still continue to operate; after an APF fails and exits, the remaining APFs can respond quickly and automatically distribute 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] Non-linear load parameters:

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

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

[0080] The inverter AC side output filter inductor L1 = L2 = L3 = 2.5mH, 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, MAF sliding window time length T 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 put into use, the grid-side current waveform and FFT analysis results are as follows: Figure 4 As shown, the total harmonic distortion is as high as 42.04%, mainly the 3rd, 5th, 7th and 9th harmonics.

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

[0086] If the primary control unit and communication are normal, K is calculated according to formula (4) ff =11 / 30, such as Figure 5 As shown in (a), the output currents of the three APFs are exactly the same, and the grid-side current THD drops from 42.04% to 1.15%, with a good governance 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 currents of the three APFs are still exactly the same, and the grid-side current THD drops from 42.04% to 7.18%. The system compensation accuracy decreases, but each APF can still automatically allocate the compensation current according to the rated capacity ratio.

[0088] If APF2 stops running due to a fault, the remaining APFs continue to operate normally, such as Figure 5 As shown in (c), the output currents of APF1 and APF3 remain consistent, the grid-side current THD drops from 42.04% to 1.23%, the system responds quickly, and the fault transition time is short.

[0089] Condition 2: When the rated capacities of the three APFs are different, I1=I2=120A, I3=60A; then I max =120A, set D1=D2=D according to formula (1) max =0.1, D3=1.2;

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

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

[0092] If APF2 stops running due to a fault, the remaining APFs continue to operate normally, such as Figure 6 As shown in (c), the output currents of APF1 and APF2 are exactly the same, the output current of APF3 is half of that of APF1, and the grid-side current THD drops from 42.04% to 1.20%. The system responds quickly and the fault transition time is short.

[0093] Example 2

[0094] Embodiment 2 of the present invention provides a control system corresponding to the above-mentioned embodiment 1, 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 the above-mentioned embodiment 1.

[0095] In some implementations, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory, such as at least one disk memory.

[0096] In some other implementations, the processor may be a central processing unit (CPU), a digital signal processor (DSP), or other general-purpose processors of various types, which are not limited herein.

[0097] Example 3

[0098] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to the above embodiment 1, on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the method of the above embodiment 1 are implemented.

[0099] Computer readable storage media can be tangible devices that hold and store instructions used by instruction execution devices. Computer readable storage media can be, for example, but not limited to, electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any combination thereof.

[0100] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt 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.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0101] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0102] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0103] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0104] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these 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, which are connected in parallel to a power grid, and each APF comprises 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, The following steps are involved: Determine the APF with the largest rated capacity among N APFs. Suppose the rated capacity of this APC is I max , whose feedback coefficient is D max , 0≤D max ≤1; Set the feedback coefficient of other APF to D n , subscript n represents the nth APF, 1≤n≤N; Extract the grid voltage V PCC The phase angle θ and the grid-side current i s The dq-axis harmonic component i sdf 、i sqf , load side current i L The dq-axis harmonic component i Ldh ,i Lqh 、The AC output current i of the nth APF cn The dq-axis harmonic component i cndh ,i cnqh ; When the central controller works normally and the communication is normal, the feedforward coefficient K is transmitted by the central controller. ff ; When the central controller fails or the communication fails, the feedforward coefficient K is given ff =0; Using the APF feedback coefficient and grid-side current i s The dq-axis harmonic components and load-side current i L The dq-axis harmonic components and the AC output current i of the nth APF cn The dq axis harmonic component calculation reference dq axis harmonic component i cndh_ref ,i cnqh_ref : The DC side capacitor voltage v dcn and DC voltage reference value v dcn_ref After comparison, the difference is passed through the PI controller to obtain the fundamental active component i cndf_ref ; Using the fundamental wave active component i cndf_ref , feedforward coefficient, feedback coefficient of the nth APF to obtain the reactive current component i to be compensated cnqf_ref ; Calculate the output current dq axis reference component i cnd_ref ,i cnq_ref ; The output current dq axis reference component i cnd_ref ,i cnq_ref After the inverse Park transformation, the current signal in the stationary coordinate system is obtained, and after the current limiting link, the output current reference signal i is obtained. cn_ref ; will i cn_ref with i cn After comparison, the difference passes through the PR controller and then adds the grid voltage V PCC Feedforward to obtain the inverter modulation wave signal, and obtain the inverter switch trigger signal by sinusoidal pulse width modulation to drive the inverter to work.

2. The APF multi-machine parallel system control method according to claim 1, characterized in that: Feedback coefficient D of the nth APF n The calculation formula is: Among them, I cn Indicates 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 the grid voltage V PCC The phase angle θ and the grid-side current i s The dq-axis harmonic components and 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: s Through Park transformation, we can get the dq axis component i in the fundamental frequency rotating coordinate system. sd 、i sq , use the moving average filter to extract the dq axis fundamental component i sdf 、i sqf , and further obtain the dq-axis harmonic component i sdh =i sd -i sdf 、i sqh =i sq -i sqf , similarly L The dq-axis harmonic component i Ldh ,i Lqh and i cn The dq-axis harmonic component i cndh ,i cnqh .

4. The APF multi-machine parallel system control method according to claim 3 is characterized in that: The transfer function of the sliding average filter is: Where T w is the sliding window time length, and 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 Indicates 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 component i cndh_ref ,i cnqh_ref The calculation formula is: Wherein, K is the harmonic current control gain.

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