Micro-grid and weak input source pre-synchronization matching control strategy

Abstract

The invention discloses a micro-grid and weak input source pre-synchronization matching control strategy, which comprises the following steps of: 1, calculating a micro-grid frequency f * matched with a weak input source by using an f ring; 2, calculating a micro-grid phase omega t * matched with the weak input source by using a theta ring; and step 3, calculating the micro-grid voltage Vd * matched with the weak input source by using the V ring. Through independent control loops and update reference commands, mutual influence among the loops is avoided, system stability is improved, propagation of frequency, phase and voltage errors is reduced, initial jump and voltage transient are avoided by adopting an integral controller, loop stability is ensured, gain and stabilization time are optimized, and the stability of the system is improved. And the frequency, the phase and the voltage are quickly and accurately synchronized.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a strategy for weak source pre-synchronization of a microgrid. Background Art

[0002] A microgrid is a small power system consisting of distributed energy resources (such as solar energy, wind energy), energy storage devices and loads, which can operate independently or connect to the main grid. When connected to the grid or alternative grid forming source (AGFS), the microgrid must coordinate its own frequency, phase and voltage to match the parameters of the external grid to ensure seamless grid connection or switching. Grid-forming (GF) technology achieves frequency and voltage regulation of the grid through voltage source converter (VSC), which is particularly important in the absence of traditional grid support. The voltage source converter of the microgrid can act as the main device of the grid, providing stable power output for the microgrid and ensuring synchronization when connected to the grid or AGFS. However, current control technology faces certain challenges in handling these dynamic adjustments, especially in terms of speed and accuracy. Traditional control methods (such as proportional-integral (PI) control, synchronization algorithms, etc.) usually cannot provide a fast enough response, which easily leads to transient instability, phase jumps or oscillations in the frequency, phase and voltage matching process, especially when the input source is weak or disturbed. These problems are more obvious. Summary of the invention

[0003] The present invention proposes a novel pre-synchronization control strategy, which aims to improve the response speed and accuracy of the microgrid when it is connected to the power grid or an alternative power grid. This pre-synchronization control technology can respond more quickly to changes in frequency and phase during the grid formation process, thereby ensuring that there is no obvious transient phenomenon when the microgrid is connected to the external power grid, and the grid connection process is smoother and more stable.

[0004] The present invention is achieved by the following technical means:

[0005] A microgrid and weak input source pre-synchronization matching control strategy, comprising:

[0006] Step 1: Use the f loop to calculate the microgrid frequency f that matches the weak input source * ;

[0007] Step 2: Use the θ loop to calculate the microgrid phase ωt that matches the weak input source * ;

[0008] Step 3: Use the V loop to calculate the microgrid voltage V that matches the weak input source d * .

[0009] The microgrid frequency f in step 1 * , is the weak input source frequency f obtained by measurement G With the microgrid frequency f * First, do the difference to get the frequency error f between the two e , by f e The deviation Δf required to generate the microgrid frequency is different from the nominal frequency f nom Add them together to get G The updated f that matches * ;

[0010] The specific formula is as follows:

[0011]

[0012] f *k =f nom +△f k .

[0013] The θ loop obtains the measured weak input source phase ωt G , and then with the microgrid phase ωt * The phase error θ between the two is obtained by making a difference e , the phase error θ e Send to the integral controller to execute 1-cosθ e , and then get the deviation δ required for the microgrid phase, add the deviation value to the real-time phase of the microgrid, and get the phase difference with ωt G Matching updated ωt * ;

[0014] The specific formula is as follows:

[0015]

[0016] The real-time phase of the microgrid is calculated from the microgrid frequency, specifically 2πf * t.

[0017] The V loop obtains the measured weak input source voltage V dG , and then with the microgrid voltage V d * The error V is obtained by subtracting de , and then get the required deviation △V of the microgrid voltage d , the deviation from the nominal voltage V dnom Add together and get V dG Matching updated V d * ;

[0018] The specific formula is as follows:

[0019]

[0020] The open-loop transfer function of the f-loop is (k pf +k if / s), where k pf =0.1, k if =1000, the open-loop transfer function of the θ loop is [(k iδ / s)(1-cosθ e )], where k iδ =50.

[0021] The closed-loop transfer function T(s) of the f-loop is obtained as follows:

[0022]

[0023] The stabilization time of the f-loop and V-loop is set to 4ms, and the stabilization time of the θ-loop is 40ms; for a maximum phase error θ of ±180°, the obtained f-loop and V-loop PI gains are (0.1; 1000), and the θ-loop I gain is 50.

[0024] The present invention avoids mutual influence between loops through independent control loops and updated reference commands, improves system stability, reduces the propagation of frequency, phase and voltage errors, adopts an integral controller to avoid initial jumps and voltage transients, ensures loop stability, optimizes gain and stabilization time, and quickly and accurately synchronizes frequency, phase and voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the master-slave control AC microgrid structure;

[0026] Figure 2 Schematic diagram of the pre-synchronization control strategy of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0028] The present invention relates to a microgrid and a weak input source pre-synchronization matching control strategy, comprising:

[0029] Step 1: Use the f loop to calculate the microgrid frequency f that matches the weak input source * ;

[0030] Step 2: Use the θ loop to calculate the microgrid phase ωt that matches the weak input source * ;

[0031] Step 3: Use the V loop to calculate the microgrid voltage V that matches the weak input source d * .

[0032] The microgrid frequency f in step 1 * , is the weak input source frequency f obtained by measurement G With the microgrid frequency f * First, do the difference to get the frequency error f between the two e , by f e The deviation Δf required to generate the microgrid frequency is different from the nominal frequency f nom Add them together to get G The updated f that matches * ;

[0033] The specific formula is as follows:

[0034]

[0035] f *k =f nom +△f k .

[0036] The θ loop obtains the measured weak input source phase ωt G , and then with the microgrid phase ωt * The phase error θ between the two is obtained by making a difference e , the phase error θ e Send to the integral controller to execute 1-cosθ e , and then get the deviation δ required for the microgrid phase, add the deviation value to the real-time phase of the microgrid, and get the phase difference with ωt G Matching updated ωt * ;

[0037] The specific formula is as follows:

[0038]

[0039] The real-time phase of the microgrid is calculated from the microgrid frequency, specifically 2πf * t.

[0040] The V loop obtains the measured weak input source voltage V dG , and then with the microgrid voltage V d * The error V is obtained by subtracting de , and then get the required deviation △V of the microgrid voltage d , the deviation from the nominal voltage V dnom Add together and get V dG Matching updated V d * ;

[0041] The specific formula is as follows:

[0042]

[0043] The open-loop transfer function of the f-loop is (k pf +k if / s), where k pf =0.1, k if =1000, the open-loop transfer function of the θ loop is [(k iδ / s)(1-cosθ e )], where k iδ =50.

[0044] The closed-loop transfer function T(s) of the f-loop is obtained as follows:

[0045]

[0046] The stabilization time of the f-loop and V-loop is set to 4ms, and the stabilization time of the θ-loop is 40ms; for a maximum phase error θ of ±180°, the obtained f-loop and V-loop PI gains are (0.1; 1000), and the θ-loop I gain is 50.

Claims

1. A microgrid and weak input source pre-synchronization matching control strategy, characterized in that: include: Step 1: Use the f loop to calculate the microgrid frequency f that matches the weak input source * ; Step 2: Use the θ loop to calculate the microgrid phase ωt that matches the weak input source * ; Step 3: Use the V loop to calculate the microgrid voltage V that matches the weak input source d * .

2. The microgrid and weak input source pre-synchronization matching control strategy according to claim 1 is characterized in that: The microgrid frequency f in step 1 * , is the weak input source frequency f obtained by measurement G With the microgrid frequency f * First, do the difference to get the frequency error f between the two e , by f e The deviation Δf required to generate the microgrid frequency is different from the nominal frequency f nom Add them together to get G The updated f that matches * ; The specific formula is as follows: △f k =△f k-1 +k pf {f e k -f e k-1 }+k if f e k f *k =f nom +△f k 。 3. A microgrid and weak input source pre-synchronization matching control strategy according to claim 1, characterized in that: The θ loop obtains the measured weak input source phase ωt G , and then with the microgrid phase ωt * The phase error θ between the two is obtained by making a difference e , the phase error θ e Send to the integral controller to execute 1-cosθ e , and then get the deviation δ required for the microgrid phase, add the deviation value to the real-time phase of the microgrid, and get the phase difference with ωt G Matching updated ωt * ; The specific formula is as follows:

4. A microgrid and weak input source pre-synchronization matching control strategy according to claim 3, characterized in that: The real-time phase of the microgrid is calculated from the microgrid frequency, specifically 2πf * t.

5. A microgrid and weak input source pre-synchronization matching control strategy according to claim 1, characterized in that: The V loop obtains the measured weak input source voltage V dG , and then with the microgrid voltage V d * The error V is obtained by subtracting de , and then get the required deviation △V of the microgrid voltage d , the deviation from the nominal voltage V dnom Add together and get V dG Matching updated V d * ; The specific formula is as follows:

6. A microgrid and weak input source pre-synchronization matching control strategy according to claim 1, characterized in that: The open-loop transfer function of the f-loop is (k pf +k if / s), where k pf =0.1, k if =1000, the open-loop transfer function of the θ loop is [(k iδ / s)(1-cosθ e )], where k iδ =50.

7. A microgrid and weak input source pre-synchronization matching control strategy according to claim 6, characterized in that: The closed-loop transfer function T(s) of the f-loop is obtained as follows:

8. A microgrid and weak input source pre-synchronization matching control strategy according to claim 1, characterized in that: The stabilization time of the f-loop and V-loop is set to 4ms, and the stabilization time of the θ-loop is 40ms; for a maximum phase error θ of ±180°, the obtained f-loop and V-loop PI gains are (0.1; 1000), and the θ-loop I gain is 50.

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