A current compensation control method and device for a phase-locked loop type grid-connected converter system

Abstract

The application relates to a current compensation control method and device of a phase-locked loop type grid-connected converter system, and belongs to the technical field of power system control. The method comprises the following steps: acquiring the voltage of a main grid, the inductance value of a grid-side line, and the phase-locked loop control parameters of each grid-connected converter; according to the voltage, the inductance value and the phase-locked loop control parameters, calculating the critical current threshold value of each grid-connected converter injected into a common connection point, and taking the critical current threshold value as a reference current value; acquiring the real-time current value of each grid-connected converter injected into the common connection point; comparing the real-time current value with the corresponding reference current value, if the real-time current value is greater than the reference current value, calculating the current difference value between the real-time current value and the reference current value, and compensating the current difference value to the main grid, so as to complete the current compensation control; otherwise, it is determined that the operation state of the grid-connected converter system is stable, and the current compensation control is not performed on the main grid. The application improves the stability of the grid-connected converter system.

Description

Technical Field

[0001] This invention relates to the field of power system control technology, and in particular to a current compensation control method and device for a phase-locked loop grid-connected converter system. Background Technology

[0002] With the rapid development of the new energy industry, wind power, photovoltaics, and other renewable energy sources are being connected to the grid on a large scale, and the traditional power system is gradually evolving into a new type of power system dominated by new energy sources. Compared with the traditional power system dominated by synchronous units such as thermal power and hydropower, the new power system mainly relies on grid-connected converters to achieve grid access for new energy power generation equipment.

[0003] In scenarios with a high proportion of renewable energy connected to the grid, the proportion of synchronous generators decreases significantly, the grid short-circuit capacity is significantly reduced, and the system inertia and main grid voltage support capability continue to weaken. The AC grid as a whole exhibits typical characteristics of a weak grid operation. Under weak grid conditions, the grid impedance increases significantly, no longer possessing the rigid voltage support characteristics of a traditional strong grid. A strong coupling interaction exists between the dynamic response process of the grid-connected converter and the grid operating state. Specifically, the control dynamics and response characteristics of the grid-connected converter itself are coupled and interfere with the impedance characteristics of the weak grid, easily leading to abnormal fluctuations in the interactive current between the grid-connected converter and the main grid. This can result in problems such as a significant increase in current, frequent oscillations, and even overcurrent, subsequently causing serious operational failures such as oscillations and instability in the grid-connected converter system. Such instability problems directly disturb the voltage and frequency stability of the local grid and even the entire power system, seriously threatening the safe, stable, and reliable operation of the new power system and restricting the large-scale grid connection and efficient consumption of renewable energy generation.

[0004] Currently, existing power system stability control technologies and grid-connected converter regulation strategies cannot effectively adapt to the operating characteristics of weak power grids, cannot fundamentally suppress system instability caused by the interaction between grid-connected converters and weak power grids, and cannot solve the problem of insufficient grid stability in scenarios with a high proportion of new energy grid connection, thus exhibiting significant technical limitations. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problems of poor adaptability to the weak grid operation scenario of new power systems and the inability to effectively suppress current oscillations and system instability caused by the dynamic coupling between the grid-connected converter and the grid in the existing technology.

[0006] In a first aspect, to solve the above-mentioned technical problems, the present invention provides a current compensation control method for a phase-locked loop grid-connected converter system, comprising: S1. The grid-connected converter system includes a main grid, grid-side lines, and multiple grid-connected converters; the voltage of the main grid, the inductance value of the grid-side lines, and the phase-locked loop control parameters of each grid-connected converter are obtained; S2. Calculate the critical current threshold injected into the common connection point of each grid-connected converter based on the voltage, the inductance value and the phase-locked loop control parameters, and use the critical current threshold as the reference current value. S3. Obtain the real-time current value injected into the common connection point of each grid-connected converter; compare the real-time current value with the corresponding reference current value; if the real-time current value is greater than the reference current value, calculate the current difference between the real-time current value and the reference current value, and compensate the current difference to the main grid to complete the current compensation control; otherwise, determine that the grid-connected converter system is in a stable operating state, and do not perform current compensation control on the main grid.

[0007] In one embodiment of the present invention, step S3, in the process of obtaining the real-time current value injected into the common connection point of each grid-connected converter, further includes obtaining the phase angle of the injected common connection point of each grid-connected converter, and using the phase angle as the compensation control phase angle.

[0008] In one embodiment of the present invention, the expression for the critical current threshold is: ; in, Indicates the first The d-axis value of the current injected into the point of common coupling of the grid-connected converter; , All indicate the first Phase-locked loop control parameters of the grid-connected converter; Indicates the main grid voltage. This indicates the inductance value of the grid-side line. Indicates the total number of grid-connected converters. This represents the ratio of the line impedance on the grid-connected converter side to the line impedance on the grid side. Indicates the first Steady-state initial phase difference of the grid-connected converter This represents the disturbance value.

[0009] In one embodiment of the present invention, in step S3, the expression for the current difference is: ; in, , They represent the first The d and q values ​​of the current difference; , They represent the first d-axis limiting and q-axis limiting of each reference current value; , They represent the first The d and q values ​​of the real-time current.

[0010] In one embodiment of the invention, all the grid-connected converters are connected to a common connection point on their respective output sides and connected to the same busbar via the same line.

[0011] Secondly, to solve the above-mentioned technical problems, the present invention provides a current compensation control device for a phase-locked loop (PLL) grid-connected converter system, used to implement the above-mentioned current compensation control method for a PLL grid-connected converter system, comprising: The acquisition module is used to acquire the voltage of the main grid, the inductance value of the grid-side lines, and the phase-locked loop control parameters of each grid-connected converter; wherein, the grid-connected converter system includes the main grid, the grid-side lines, and multiple grid-connected converters; The calculation module is used to calculate the critical current threshold injected into the common connection point of each grid-connected converter based on the voltage, the inductance value and the phase-locked loop control parameters, and use the critical current threshold as a reference current value; The compensation control module is used to acquire the real-time current value injected into the common connection point of each grid-connected converter; compare the real-time current value with the corresponding reference current value; if the real-time current value is greater than the reference current value, calculate the current difference between the real-time current value and the reference current value, and compensate the main grid for the current difference to complete the current compensation control; otherwise, determine that the grid-connected converter system is in a stable operating state, and do not perform current compensation control on the main grid.

[0012] In one embodiment of the present invention, a control circuit is further included, the control circuit including a limiting unit and a regulator; the real-time current value enters the limiting unit for amplitude constraint and difference calculation and then enters the regulator.

[0013] In one embodiment of the present invention, the control circuit further includes a modulation unit and a coordinate transformation unit. The voltage component output by the regulator is input to the modulation unit to obtain the dq-axis modulation coefficient. The dq-axis modulation coefficient is input to the coordinate transformation unit to generate a three-phase modulation signal.

[0014] In one embodiment of the present invention, an outer loop controller is further connected to the compensation control module, and the current difference is the input of the outer loop controller.

[0015] In one embodiment of the present invention, each of the plurality of grid-connected converters includes a phase-locked loop, and the compensation control module uses the phase-locked loop to obtain the phase angle of the injection common connection point corresponding to the grid-connected converter.

[0016] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: (1) The current compensation control method and device for a phase-locked loop (PLL) grid-connected converter system described in this invention calculates the critical current threshold of the point of common coupling (PCC) based on the main grid voltage, line inductance, and PLC control parameters of each grid-connected converter. The stable boundary that closely matches the actual operating conditions is used as the compensation reference current, effectively solving the problem of insufficient adaptability of traditional empirical fixed thresholds. This invention can adapt to scenarios where multiple converters operate in parallel. The invention compares the measured grid-connected current at the PCC with the reference threshold in real time, and only performs precise compensation for the difference in current exceeding the limit. The device only operates when the current exceeds the limit and automatically goes into hibernation under steady-state conditions. The entire control chain is simple and responds quickly, constraining the grid-connected current within a safe and stable range, cutting off the instability path caused by the interaction between the converter and the grid under weak grid conditions, and ensuring the safe operation of the power system.

[0017] (2) The present invention can avoid secondary disturbances to the power grid caused by overcompensation and reduce the operating losses of the energy storage unit. The device does not require large-scale hardware modification of existing equipment, has low engineering implementation difficulty and good scalability, and has high application value in new weak power grids with a high proportion of new energy access. It can significantly improve the operating stability of the grid-connected converter system and the grid-connected absorption capacity of new energy. Attached Figure Description

[0018] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0019] Figure 1 This is a flowchart of a current compensation control method for a phase-locked loop grid-connected converter system according to a preferred embodiment of the present invention; Figure 2 This is a block diagram of the grid-connected converter system used in a preferred embodiment of the present invention; Figure 3 This is a block diagram of the grid-connected converter system and the current compensation control used during instability in a preferred embodiment of the present invention; Figure 4 This is a control block diagram of a current compensation control device for a phase-locked loop grid-connected converter system according to a preferred embodiment of the present invention; Figure 5 This is a frequency simulation waveform diagram of a preferred embodiment of the present invention without a current compensation control device. Figure 6 The above is a frequency simulation waveform diagram of the current compensation control device implemented in a preferred embodiment of the present invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0021] Example 1: Reference Figure 1 As shown, the present invention provides a current compensation control method for a phase-locked loop grid-connected converter system, including but not limited to the following steps: S1. The grid-connected converter system includes the main grid, grid-side lines, and multiple grid-connected converters; it acquires the voltage of the main grid, the inductance value of the grid-side lines, and the phase-locked loop control parameters of each grid-connected converter. S2. Calculate the critical current threshold injected into the common connection point of each grid-connected converter based on the voltage, inductance value and phase-locked loop control parameters, and use the critical current threshold as the reference current value. S3. Obtain the real-time current value injected into the common connection point of each grid-connected converter; compare the real-time current value with the corresponding reference current value. If the real-time current value is greater than the reference current value, calculate the current difference between the real-time current value and the reference current value, and compensate the current difference to the main grid to complete the current compensation control; otherwise, determine that the grid-connected converter system is in a stable operating state and do not perform current compensation control on the main grid.

[0022] The current compensation control method for a phase-locked loop (PLL) grid-connected converter system described in this invention quantitatively solves the critical current threshold of the point of common coupling (PCC) using the main grid voltage, line inductance, and PLL control parameters of each grid-connected converter. Using this actual operating condition stability boundary as the compensation reference current, it effectively avoids the poor adaptability problem caused by empirically fixed thresholds and can be adapted to multi-converter parallel scenarios on a per-unit basis. By comparing the measured grid-connected current with the reference threshold in real time, precise compensation is only applied to the difference in current exceeding the limit. Compensation is only initiated when the current exceeds the limit, and automatic sleep occurs in steady state. The control link is simple and has a fast response speed. It can constrain the PCC grid-connected current within the stable range, block the unstable path of converter-grid interaction under weak grid conditions, and ensure the safe and stable operation of the power system. Simultaneously, it avoids secondary grid disturbances caused by overcompensation, reduces continuous operating losses of energy storage units, requires no large-scale hardware modifications, has low engineering implementation difficulty, and strong scalability. It has extremely high application value in new weak grid scenarios with a high proportion of new energy grid integration.

[0023] Specifically, refer to Figure 2As shown, the grid-connected converter system mainly consists of a main grid, multiple grid-connected converters, and their connecting lines. All grid-connected converters are connected to their respective output side's Point of Common Coupling (PCC) and connected to the same bus via the same lines. Each grid-connected converter collects the voltage and current at its respective PCC point and uses this data for its control circuit. The control circuit of the grid-connected converter mainly includes a phase-locked loop (PLL) and a dual-loop control system. The PLL is used for the grid-connected converter to track the phase angle of the main grid, while the dual-loop control circuit is used to control the output current of the voltage source converter (VSC).

[0024] Furthermore, Figure 2 The grid-connected converter system was demonstrated, including In the case of grid-connected converters, where the symbol... Indicates the first Taiwan converter terminal voltage, symbol Indicates the first The current in the branch of the grid-connected converter, Indicates the first AC side port / grid connection point of Taiwan voltage source converter.

[0025] Specifically, in step S2, the critical current threshold at the PCC point when the grid-connected converter system experiences instability is obtained, wherein the estimation expression for the critical current threshold is: ; in, ( ) indicates the first The d-axis value of the current injected into the point of common coupling of the grid-connected converter; , All indicate the first Phase-locked loop control parameters of the grid-connected converter; Indicates the main grid voltage. This indicates the inductance value of the grid-side line. This indicates the total number of grid-connected converters connected to the grid-connected converter system. This represents the ratio of the line impedance on the grid-connected converter side to the line impedance on the grid side. Indicates the first Steady-state initial phase difference of the grid-connected converter; This represents the disturbance value, i.e., the th Phase disturbance deviation (dynamic phase offset) of the converter.

[0026] Furthermore, the disturbance value The mathematical expression is: ; in, This indicates the moment when the disturbance occurs (initial time 0). The actual operating position difference of the converter is the instantaneous phase value after the disturbance.

[0027] Step 2 ensures that the current injected into the grid by the grid-connected VSC is constrained within a given limit, thereby preventing the grid-connected converter system from becoming unstable. For currents exceeding the limit or exhibiting deficits, the current compensation control method described in this invention absorbs and compensates for them. Furthermore, setting the critical current threshold as the reference current value for the grid-connected converter in the current compensation control device prepares the outer loop controller of the current compensation control device involved in this invention. The current compensation control device, which is the hardware execution carrier of the control method of this invention, is an energy storage device.

[0028] Furthermore, regarding the ratio of the line impedance on the grid-connected converter side to the line impedance on the grid side... This coefficient will be selected with different values ​​depending on the actual power grid topology. Specifically, if the line on the grid-connected converter side is an in-site line, and its distance is shorter than that of the grid-side line, then when calculating the critical value for current instability, the ratio will be... If both the converter-side lines and the grid-side lines are internet access lines, and the PCC point of the grid-connected converter is connected to the output side, the selection should be based on the actual scenario. This embodiment mainly simulates the first scenario, therefore... Set to 1. Considering the injected current direction of the grid-connected converter is the same before and after the disturbance, the most extreme scenario is that the reference injected current of the grid-connected converter changes from 0 to the limit value where the grid-connected converter has a static equilibrium point. At this point, the disturbance value... Maximum, is ,in, This represents the symbol for pi. Therefore, Set as Based on the above settings, when the number of grid-connected converters required by the system is determined, the critical current threshold can be determined. This result represents the upper limit of the instability current value. When the injected current is negative, the same analysis can be performed, and this result can be used as the lower limit.

[0029] Specifically, in step S3, the process of obtaining the real-time current value injected into the common connection point of each grid-connected converter also includes obtaining the phase angle injected into the common connection point of each grid-connected converter, and using the phase angle as the compensation control phase angle.

[0030] Further, in step S3, the expression for the current difference is: ; in, , They represent the first The d and q values ​​of the current difference; This indicates a current limiting mechanism, using the critical current threshold obtained in step S2 as the reference current value. , They represent the first d-axis limiting and q-axis limiting of each reference current value; , These represent the first and second generations in the grid-connected converter system. The d and q values ​​of the real-time current at each PCC point.

[0031] The current compensation control method described in this embodiment can effectively solve the problem of system instability in new energy grid-connected scenarios such as wind power generation, photovoltaic power generation, energy storage, and hydrogen production, which mainly rely on grid-connected converters.

[0032] The current compensation control strategy provided by this invention uses a parallel energy storage device to absorb or compensate for excessive or insufficient current values ​​in the grid-connected converter. The control scheme is mainly implemented through the coordinated operation of three functional modules: a controller reference current acquisition module, a phase-locked loop (PLL) output phase acquisition module, and an energy storage-based current compensation control device. The specific control flow is as follows: the critical current threshold injected into the point of common coupling (PCC) of the grid-connected converter is calculated; the controller reference current acquisition module acquires the current value injected into the PCC; the PLL output angle acquisition module acquires the phase angle of the PCC; and the energy storage-based current compensation control device takes corresponding actions by comparing the injected current at the PCC with the critical current threshold. When the real-time current at the PCC exceeds the critical current threshold, the current compensation control device injects the difference between the critical current value and the real-time current value into the PCC. Through the above design, the current compensation control method proposed in this invention can effectively improve the stability of the grid-connected converter system, thereby improving the absorption capacity of the grid-connected converter system.

[0033] Example 2: Based on the same inventive concept, this embodiment provides a current compensation control device for a phase-locked loop grid-connected converter system. The principle of solving the problem is similar to the current compensation control method for a phase-locked loop grid-connected converter system provided in Embodiment 1, and the repeated parts will not be described again.

[0034] This embodiment provides a current compensation control device for a phase-locked loop (PLL) grid-connected converter system, used to implement the current compensation control method for a PLL grid-connected converter system described in Embodiment 1, including: The acquisition module is used to acquire the voltage of the main grid, the inductance value of the grid-side lines, and the phase-locked loop control parameters of each grid-connected converter; wherein, the grid-connected converter system includes the main grid, the grid-side lines, and multiple grid-connected converters; The calculation module is used to calculate the critical current threshold injected into the common connection point of each grid-connected converter based on the voltage, inductance value and phase-locked loop control parameters, and to use the critical current threshold as the reference current value. The compensation control module is used to acquire the real-time current value injected into the common connection point of each grid-connected converter; compare the real-time current value with the corresponding reference current value; if the real-time current value is greater than the reference current value, calculate the current difference between the real-time current value and the reference current value, and compensate the current difference to the main grid to complete the current compensation control; otherwise, determine that the grid-connected converter system is operating stably and do not perform current compensation control on the main grid.

[0035] Specifically, refer to Figure 3 As shown, the current compensation control device in this embodiment adopts the same grid-connected topology as the grid-connected converter system. The two have basically the same hardware main circuit grid-connected architecture. The core difference lies in the control logic and regulation strategy of the built-in control circuit.

[0036] Specifically, refer to Figure 3 and Figure 4 As shown, the current compensation control device in this embodiment further includes a control circuit, which includes a limiting unit and a regulator; the real-time current value enters the limiting unit for amplitude constraint and difference calculation before entering the regulator. In this embodiment, the regulator is preferably a PI regulator.

[0037] Furthermore, the control circuit also includes a modulation unit and a coordinate transformation unit. The voltage component output by the regulator is input to the modulation unit to obtain the dq-axis modulation coefficient; the dq-axis modulation coefficient is input to the coordinate transformation unit to generate a three-phase modulation signal.

[0038] Specifically, the current compensation control device described in this embodiment further includes an outer loop controller connected to the compensation control module, with the current difference value being the input to the outer loop controller. The design of the outer loop controller is essentially the calculation expression for the current difference value.

[0039] Specifically, the current compensation control device in this embodiment is similar to the VSC structure in the grid-connected converter system. However, the current compensation control device does not have a separate phase-locked loop (PLL); the controller phase angle is derived from the original grid-connected converter's PLL. Specifically, multiple grid-connected converters include PLLs, and the compensation control module uses the PLLs to obtain the phase angle of the corresponding grid-connected converter's injection point of common connection. This phase angle is used as the controller phase angle of the current compensation control device's control circuit in this embodiment. This design ensures that the angle difference between the current compensation control device and the grid-connected converter is zero.

[0040] Furthermore, the critical current threshold obtained by the calculation module is set as the reference current value of VSC in the current compensation control device of this embodiment. The real-time current value of the PCC point in the grid-connected converter system. , , and the corresponding reference current value , In contrast, when the real-time current value is greater than the reference current value, the current compensation control device activates and compensates for the current difference between the reference current value and the real-time current value in parallel with the main grid. Conversely, the current compensation control device does not operate when the real-time current value is less than the reference current value.

[0041] Specifically, refer to Figure 3 and Figure 4 As shown, the overall control circuit of the grid-connected converter system and the current compensation control device described in this embodiment is: an AC ideal voltage source. Equivalent impedance of series power grid Output total grid current It connects to the common bus, and the common bus branches out two parallel branches. The two parallel branches are as follows: First branch: series circuit impedance Connect to the AC side port of the grid-connected converter (voltage source converter, VSC). The AC terminal voltage and current of the converter are respectively... , ; The second branch: directly connected to the AC side port of the current compensation control device (another VSC converter).

[0042] Total grid current The current is shunted at the BUS node, becoming the current in the grid-connected converter branch. It works in conjunction with the branch current of the current compensation control device to achieve coordinated regulation of bus power and current.

[0043] Furthermore, in the grid-connected converter system, the converter terminal voltage is collected. The signal is fed into a phase-locked loop (PLL), and the PLL outputs a synchronized phase. Compared with the reference angular velocity This provides a synchronous rotating coordinate system angular reference for coordinate transformation. The outer loop controller of the current compensation control device is located inside the grid-connected converter system. The outer loop controller outputs a d-axis current reference value. q-axis current reference value In the d-axis current loop, the reference value is... Subtract the actual feedback d-axis current The difference is fed into the PI regulator, and the output voltage component... Superimposed decoupling terms d-axis voltage feedforward at the machine terminal Then divide by the DC side voltage The d-axis modulation coefficient is obtained. In the q-axis current loop, the reference value is... Subtract the actual feedback q-axis current The difference is fed into the PI regulator, and the output voltage component... Superimposed decoupling terms q-axis voltage feedforward at the machine terminal Then divide by the DC side voltage The q-axis modulation coefficients are obtained. For inverse coordinate transformation, the dq-axis modulated signal, combined with the synchronization phase... After inverse dq / abc coordinate transformation, a three-phase modulated signal is generated. This data is fed into the converter's internal drive logic, ultimately controlling the on / off state of the grid-connected VSC power devices. Furthermore, regarding the PLL's internal structure, the terminal voltage... After abc / dq coordinate transformation, the signal is fed into a PI controller, and the PI output is superimposed with the rated angular velocity. The integral stage integrates at 1 / s and outputs a phase-locked phase. This forms a synchronous rotating phase-locked loop.

[0044] Furthermore, in the current compensation control device described in this embodiment, a voltage source grid-connected converter is also used, employing current closed-loop control with output limiting, and multiplexing the synchronous phase output of the grid-connected converter PLL. Coordinate system synchronization is achieved. The d-axis and q-axis current reference values ​​are first subjected to amplitude limiting to prevent the commanded current from exceeding limits. In d-axis control, the limited reference value is successively subtracted by two levels of deviation (first-level deviation is the difference after limiting the reference value, and second-level deviation is the difference after subtracting the actual feedback current). The error is fed into the PI regulator; the output voltage components are superimposed with decoupling terms. Current compensation control device terminal voltage feedforward Divide by DC voltage Obtain the d-axis modulation coefficient In q-axis control, the reference value after limiting is successively subtracted by two levels of deviation (first-level deviation is the difference after limiting the reference value, and second-level deviation is the difference between the reference value and the actual feedback current). The error is fed into the PI regulator; the output voltage components are superimposed with decoupling terms. Compensation control device terminal voltage feedforward Divide by DC voltage Obtain the q-axis modulation coefficient . , Combined with shared phase-locked angle Perform an inverse dq / abc transform to output a three-phase modulated signal. The power converter of the drive current compensation control device realizes dynamic compensation of bus current harmonics, reactive power and unbalanced components.

[0045] It should be noted that, in Figure 3 In the context of the grid-connected converter system and the current compensation control device, the d-axis modulation coefficients are... q-axis modulation coefficient and three-phase modulation signal Although the same symbols are used in the attached diagrams, the specific values ​​are different; the two calculate and generate modulation signals through their respective independent control loops, and drive the corresponding voltage source converters respectively.

[0046] Furthermore, the present invention is applicable to grid-connected converter systems, and is therefore suitable for solving the instability problem of systems in various new energy grid-connected scenarios such as wind power generation, photovoltaic power generation, energy storage, and hydrogen production that are mainly based on grid-connected converters. It is not limited to the number of VSCs, as long as each VSC is equipped with a current compensation control device.

[0047] Furthermore, this embodiment uses a wind power hydrogen production project as an example to conduct an experiment to verify the practical application effect of this current compensation control device. The experimental system consists of an external main grid, three wind turbines, and a hydrogen production power supply. During the experiment, the operating parameters were first gradually adjusted to determine the critical current threshold corresponding to the instability of the grid-connected converter system; after further increasing the grid current, the system exhibited a significant instability state, and the relevant operating waveforms are shown below. Figure 5 As shown in the figure. After installing the current compensation control device described in this invention on three wind turbines, the system operation returned to stability, and the instability phenomenon was completely eliminated. The test results are as follows. Figure 6 As shown. This demonstrates that the present invention can effectively suppress the instability problem of grid-connected converter systems caused by abnormal current, and the control effect is significant. Among them, Figure 5 and Figure 6 The vertical axis represents angular velocity, with units of rad·s. -1 (radians per second).

[0048] 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 embodied 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.

[0049] 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.

[0050] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0051] 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.

[0052] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A current compensation control method for a phase-locked loop grid-connected converter system, characterized in that, include: S1. The grid-connected converter system includes the main grid, grid-side lines, and multiple grid-connected converters; Obtain the voltage of the main grid, the inductance value of the grid-side line, and the phase-locked loop control parameters of each of the grid-connected converters; S2. Calculate the critical current threshold injected into the common connection point of each grid-connected converter based on the voltage, the inductance value and the phase-locked loop control parameters, and use the critical current threshold as the reference current value. S3. Obtain the real-time current value injected into the common connection point of each grid-connected converter; compare the real-time current value with the corresponding reference current value; if the real-time current value is greater than the reference current value, calculate the current difference between the real-time current value and the reference current value, and compensate the current difference to the main grid to complete the current compensation control; otherwise, determine that the grid-connected converter system is in a stable operating state, and do not perform current compensation control on the main grid.

2. The current compensation control method for a phase-locked loop grid-connected converter system according to claim 1, characterized in that, In step S3, the process of obtaining the real-time current value injected into the common connection point of each grid-connected converter also includes obtaining the phase angle of the injection into the common connection point of each grid-connected converter, and using the phase angle as the compensation control phase angle.

3. The current compensation control method for a phase-locked loop grid-connected converter system according to claim 1, characterized in that, The expression for the critical current threshold is: ； in, Indicates the first The d-axis value of the current injected into the point of common coupling of the grid-connected converter; , All indicate the first Phase-locked loop control parameters of the grid-connected converter; Indicates the main grid voltage. This indicates the inductance value of the grid-side line. Indicates the total number of grid-connected converters. This represents the ratio of the line impedance on the grid-connected converter side to the line impedance on the grid side. Indicates the first Steady-state initial phase difference of the grid-connected converter This represents the disturbance value.

4. The current compensation control method for a phase-locked loop grid-connected converter system according to claim 1, characterized in that, In step S3, the expression for the current difference is: ； in, , They represent the first The d and q values ​​of the current difference; , They represent the first d-axis limiting and q-axis limiting of each reference current value; , They represent the first The d and q values ​​of the real-time current.

5. The current compensation control method for a phase-locked loop grid-connected converter system according to claim 1, characterized in that, All of the grid-connected converters are connected to a common connection point on their respective output sides and are connected to the same bus via the same line.

6. A current compensation control device for a phase-locked loop (PLL) grid-connected converter system, used to implement the current compensation control method for a PLL grid-connected converter system as described in any one of claims 1 to 5, characterized in that, include: The acquisition module is used to acquire the voltage of the main grid, the inductance value of the grid-side lines, and the phase-locked loop control parameters of each grid-connected converter; wherein, the grid-connected converter system includes the main grid, the grid-side lines, and multiple grid-connected converters; The calculation module is used to calculate the critical current threshold injected into the common connection point of each grid-connected converter based on the voltage, the inductance value and the phase-locked loop control parameters, and use the critical current threshold as a reference current value; The compensation control module is used to acquire the real-time current value injected into the common connection point of each grid-connected converter; compare the real-time current value with the corresponding reference current value; if the real-time current value is greater than the reference current value, calculate the current difference between the real-time current value and the reference current value, and compensate the main grid for the current difference to complete the current compensation control; otherwise, determine that the grid-connected converter system is in a stable operating state, and do not perform current compensation control on the main grid.

7. The current compensation control device for a phase-locked loop grid-connected converter system according to claim 6, characterized in that, It also includes a control circuit, which includes a limiting unit and a regulator; the real-time current value enters the limiting unit for amplitude constraint and difference calculation before entering the regulator.

8. The current compensation control device for a phase-locked loop grid-connected converter system according to claim 7, characterized in that, The control circuit further includes a modulation unit and a coordinate transformation unit. The voltage component output by the regulator is input to the modulation unit to obtain the dq-axis modulation coefficient. The dq-axis modulation coefficient is input to the coordinate transformation unit to generate a three-phase modulation signal.

9. A current compensation control device for a phase-locked loop grid-connected converter system according to claim 6, characterized in that, It also includes an outer loop controller connected to the compensation control module, with the current difference being the input of the outer loop controller.

10. A current compensation control device for a phase-locked loop grid-connected converter system according to claim 6, characterized in that, Each of the grid-connected converters includes a phase-locked loop (PLL), and the compensation control module uses the PLL to obtain the phase angle of the injection common connection point corresponding to the grid-connected converter.

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