Improved VSG control method suitable for transient power angle suppression and voltage support

Abstract

The invention discloses an improved VSG control method suitable for transient power angle suppression and voltage support, and the method comprises the steps: obtaining a power angle reference value delta * and an internal potential reference value E *, and generating a reference voltage for VSG control; wherein the power angle reference value delta * is obtained by adopting a P-f control link according to the active power given value P0, the active electromagnetic power Pe and the angular frequency rated value omega0, and the internal potential reference value E * is obtained by adopting a Q-U control link according to the reactive power given value Q0, the reactive electromagnetic power Qe, the grid-connected point voltage Ut and the voltage rated value E0; if the voltage sag fault of the power grid is judged, at least one of the scheme I and the scheme II is adopted; according to the first scheme, a virtual resistance feedback link is put into a P-f control link, and power angle compensation is achieved; according to the second scheme, a virtual capacitance feedback link is put into a Q-U control link, and output voltage compensation is achieved. According to the invention, power angle divergence can be suppressed and the voltage supporting capability can be improved under the condition of considering fault current limiting.

Description

Technical Field

[0001] The present invention belongs to the field of renewable energy power generation control, and relates to a fault ride-through strategy suitable for large disturbances in a hydrogen production system, and in particular to an improved VSG control method suitable for transient power angle suppression and voltage support. Background Art

[0002] Driven by the decarbonization needs of industries such as electricity, energy, chemicals, and smelting, many countries have listed green hydrogen as an energy strategy. To ensure that the hydrogen production system does not rely on the external power grid, it can be flexibly planned according to the spatial distribution of wind and solar resources and hydrogen demand, and a grid-type virtual synchronous generator (VSG) is used to construct the voltage and frequency of the grid. When simulating the operating characteristics of synchronous generators, VSGs will also encounter transient stability problems with large disturbances, among which voltage stability and power angle stability are the most prominent.

[0003] In terms of transient voltage stability, traditional QU control will reduce the potential inside the VSG during the transient period, thereby reducing its transient stability. However, most current studies focus on parameter influences, and there are few strategies for voltage stability. Virtual capacitor output reactive power is usually used for support, which can be defined as virtual capacitor control (VC-VSG). The continuous change of the power angle is subject to the difference between the reference value and the actual value of the active power. In order to solve the problem of power angle divergence, most studies start from the perspective of reducing the power difference, and virtual resistance control (VR-VSG) is one of the important methods. In addition, adding transient damping or modifying the damping coefficient in the active control loop can improve synchronous stability and power angle stability at the same time. However, it is worth pointing out that the change of the power angle will lag behind the voltage during the fault evolution process. Current studies generally ignore the impact of the QU control loop or current limiting on the VSG. Summary of the invention

[0004] The purpose of the present invention is to provide an improved VSG control method suitable for transient power angle suppression and voltage support, which can suppress power angle divergence and improve voltage support capability while taking into account fault current limiting.

[0005] In order to achieve the above object, the solution of the present invention is:

[0006] An improved VSG control method suitable for transient power angle suppression and voltage support, comprising:

[0007] Obtain the power angle reference value δ* and the internal potential reference value E* to generate the reference voltage for VSG control; wherein the power angle reference value δ* is based on the active power given value P0, the active electromagnetic power P e , the angular frequency rated value ω0 is obtained by the Pf control link; the internal potential reference value E* is based on the reactive power given value Q0, reactive electromagnetic power Q e , grid connection point voltage U t, the voltage rating E0 is obtained by using the QU control link;

[0008] If it is determined that a voltage sag fault occurs in the power grid, at least one of Scheme 1 and Scheme 2 is adopted; wherein, Scheme 1 includes inputting a virtual resistance feedback link into the Pf control link to achieve power angle compensation; Scheme 2 includes inputting a virtual capacitor feedback link into the QU control link to achieve output voltage compensation.

[0009] Among them, the power angle reference value δ* and the internal potential reference value E* are obtained to generate the reference voltage for VSG control, including:

[0010]

[0011] Where ω0 is the rated value of the angular frequency, t is the time, and E* is used as the reference voltage amplitude to generate the reference voltage for VSG control.

[0012] Wherein, the Pf control link includes:

[0013] Get the active power given value P0, active electromagnetic power P e , respectively input into the positive input terminal and the negative input terminal of the first adder;

[0014] The output end of the first adder is connected to the positive input end of the second adder, and the output end of the damping link is connected to the negative input end of the second adder;

[0015] The output end of the second adder passes through a feedback link having an inertia damping system to obtain a change in angular frequency, and the change in angular frequency is also sent to the input end of the damping link;

[0016] The change in angular frequency and the rated angular frequency value ω0 are connected to a third adder for addition, and then pass through a first integrator to obtain a power angle reference value δ*;

[0017] The expression of the Pf control link is as follows:

[0018]

[0019] Wherein, the QU control link includes:

[0020] Get the reactive power given value Q0, reactive electromagnetic power Q e , respectively input into the positive input terminal and the negative input terminal of the fourth adder;

[0021] Get the voltage rating E0 and the grid connection point voltage U t , respectively input into the positive input terminal and the negative input terminal of the fifth adder;

[0022] The output ends of the fourth adder and the fifth adder are respectively subjected to the reactive coefficient kq , voltage coefficient k u The output is amplified and connected to a sixth adder for addition operation and then sent to a second integrator;

[0023] The output of the second integrator and the voltage rated value E0 are connected to a seventh adder for addition operation to obtain an internal potential reference value E*.

[0024] The expression of the QU control link is as follows:

[0025] E*=E0+[k q (Q0-Q e )+k u (E0-U t )] / s

[0026] Wherein, the expression of the virtual resistance feedback link is:

[0027]

[0028] Among them, G(R V ) is the transfer function of the virtual resistor feedback link; U t is the grid voltage, U g is the grid side voltage, δ is the power angle, X g is the grid side inductance, R v is a virtual resistor.

[0029] Wherein, the expression of the virtual capacitor feedback link is:

[0030] G(C V )=ω0Z f C v U t

[0031] Among them, G(C V ) is the transfer function of the virtual capacitor feedback link; ω0 is the rated value of the angular frequency, Z f is the VSG outlet impedance, C v is the virtual capacitor, U t is the grid connection point voltage.

[0032] An improved VSG control system suitable for transient power angle suppression and voltage support, comprising:

[0033] Pf control link is used to control the active power given value P0 and active electromagnetic power P e , the angular frequency rated value ω0 is used to obtain the power angle reference value δ*;

[0034] The QU control link is used to control the reactive power given value Q0 and reactive electromagnetic power Q e , grid connection point voltage Ut , the voltage rated value E0 is used to obtain the internal potential reference value E*;

[0035] A reference voltage generation module, used to generate a reference voltage for VSG control according to a power angle reference value δ* and an internal potential reference value E*;

[0036] The virtual resistance feedback link is used to select and connect to the Pf control link to achieve power angle compensation when a voltage sag fault occurs in the power grid; and

[0037] The virtual capacitor feedback link is used to be selected to connect to the QU control link to achieve output voltage compensation when a voltage sag fault occurs in the power grid.

[0038] Wherein, the Pf control link includes:

[0039] Get the active power given value P0, active electromagnetic power P e , respectively input into the positive input terminal and the negative input terminal of the first adder;

[0040] The output end of the first adder is connected to the positive input end of the second adder, and the output end of the damping link is connected to the negative input end of the second adder;

[0041] The output end of the second adder passes through a feedback link having an inertia damping system to obtain a change in angular frequency, and the change in angular frequency is also sent to the input end of the damping link;

[0042] The change in angular frequency and the rated angular frequency value ω0 are connected to the third adder for addition, and then pass through the first integrator to obtain a power angle reference value δ*.

[0043] Wherein, the QU control link includes:

[0044] Get reactive power given value Q0, reactive electromagnetic power Q e , respectively input into the positive input terminal and the negative input terminal of the fourth adder;

[0045] Get the voltage rating E0 and the grid connection point voltage U t , respectively input into the positive input terminal and the negative input terminal of the fifth adder;

[0046] The output ends of the fourth adder and the fifth adder are respectively subjected to the reactive coefficient k q , voltage coefficient k u The output is amplified and connected to a sixth adder for addition operation and then sent to a second integrator;

[0047] The output of the second integrator and the voltage rated value E0 are connected to a seventh adder for addition operation to obtain an internal potential reference value E*.

[0048] Wherein, the expression of the virtual resistance feedback link is:

[0049]

[0050] Among them, G(R V ) is the transfer function of the virtual resistor feedback link; U t is the grid voltage, U g is the grid side voltage, δ is the power angle, X g is the grid side inductance, R v is a virtual resistor.

[0051] Wherein, the expression of the virtual capacitor feedback link is:

[0052] G(C V )=ω0Z f C v U t

[0053] Among them, G(C V ) is the transfer function of the virtual capacitor feedback link; ω0 is the rated value of the angular frequency, Z f is the VSG outlet impedance, C v is the virtual capacitor, U t is the grid connection point voltage.

[0054] After adopting the above scheme, the present invention reveals the adverse effects of the current limiting link on the power angle stability by revealing the transient characteristics of different QU control structures in both non-current limiting and current limiting situations. Subsequently, the present invention establishes a VSG equivalent circuit model considering fault current limiting, provides a characterization method of different QU control structures on the phasor diagram, reveals the conclusion that effective voltage support is conducive to improving transient stability, and then proposes two transient control methods, namely, improving the QU control link using virtual capacitors and improving the Pf control link using virtual resistors, to simultaneously solve the voltage support and power angle stability problems, thereby reducing the risk of fault instability. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a circuit topology diagram of the present invention;

[0056] Figure 2 It is the VSG equivalent circuit phasor diagram;

[0057] Among them, (a) is the case of no current limitation, and (b) is the case of current limitation;

[0058] Figure 3 It is a voltage equivalent curve diagram under different parameters of the present invention;

[0059] Figure 4 is the equivalent circuit diagram of the strategy proposed by the present invention;

[0060] Figure 5 It is the control strategy diagram proposed by the present invention;

[0061] Among them, (a) is the virtual resistance to improve the Pf control link, (b) is the virtual capacitance to improve the QU control link;

[0062] Figure 6 This is the experimental result diagram of different control strategies when the grid voltage drops and there is no current limiting;

[0063] Among them, (a) is the traditional VSG, (b) is the virtual capacitor type (VC-) VSG, (c) is the virtual resistor type (VR-) VSG, and (d) is the control strategy of the present invention (VCE-VSG);

[0064] Figure 7 This is the experimental result diagram of different control strategies under the condition of grid voltage drop and current limiting;

[0065] Among them, (a) is the traditional VSG, and (b) is the control strategy of the present invention (VCE-VSG). DETAILED DESCRIPTION

[0066] The technical solutions and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0067] First, Figure 1 The figure shows the circuit topology of the virtual synchronous generator grid-connected system applicable to the present invention. The DC is the access side of the hydrogen production system and is connected to the AC grid through the VSC inverter. g are the internal potential of VSG and the grid voltage respectively. t and i o is the voltage and current at the grid connection point. f ,R f ,L g and R g Represents the inductance and resistance on the VSG outlet side, and the inductance and resistance on the grid side.

[0068] First, clarify the expression of the QU control link of VSG:

[0069] E=E0+[k q (Q0-Q e )+k u (E0-U t )] / s

[0070] Among them, Q0 and E0 are reactive power set value and voltage reference value respectively. In the QU controller, the virtual electromotive force E is obtained by weighted integration of reactive power deviation and voltage amplitude deviation, k q and k u Respectively represent the reactive power coefficient and voltage coefficient and both are ≥ 0.q = 0, the QU controller is a constant voltage control; when k u = 0 is constant reactive power control; when k q *k u When ≠0, it is reactive power droop control.

[0071] In order to meet the current stress limit of power electronic devices, this embodiment adopts dq axis equal amplitude current limiter, i max is the maximum current that the inverter can accommodate, i o * is the current command generated by the voltage loop, since i o ≤i max Therefore, the grid voltage U t The terminal B will never exceed the grid voltage U g As the center of the circle, with Z g *i max The range of the circle with radius is called the current limiting circle, such as Figure 2 As shown, the expression of output current under current limiting state can be written as:

[0072]

[0073] in:

[0074]

[0075] According to the vector relationship, we can get:

[0076]

[0077] When the grid impedance is purely inductive, the power angle instability phenomenon is most likely to occur. g The direction is the positive direction of the x-axis to establish a plane rectangular coordinate system, then U g :A(U g ,0) and U t :B(x t ,y t ). t Determined by the control algorithm, it can be represented as a circle with O as the center and |OB| as the radius. Define ρ = k q / (k q +k u ),ρ∈[0,1],U t The end B of will fall on different curves under different QU control structures, which are called voltage isovalue curves, such as Figure 3 As shown:

[0078]

[0079] Where, μ=(1-ρ)*X g / ρ.

[0080] U t The voltage contour curve can reflect the reactive voltage stability characteristics during the fault period. The transient stability margin increases with the decrease of ρ, and the power angle change also changes from divergence to convergence. Constant reactive power control (ρ = 1) has the lowest transient stability margin, while constant voltage control (ρ = 0) has the best stability. The stability during reactive droop control depends on the value of ρ. Constant voltage control can control the grid connection point voltage at the rated value when the voltage changes slightly, and at the same time make the VSG output the maximum current to support the grid connection point voltage as much as possible when the voltage changes greatly. Constant reactive power control cannot reliably support U t As for reactive power voltage droop control, it is very dependent on the ρ value.

[0081] The active loop power expression of VSG can be written as:

[0082]

[0083] From the above formula, we can get that as R f Increase, P e decrease, which will result in the maximum adjustment range of the power angle curve δ mar The transient stability margin decreases gradually, and there is even a risk of power angle divergence. g With R f The effect is opposite, as R g Increase, P e Increase, δ mar The change limit range is increased, the power angle convergence speed is accelerated, and the transient stability is improved. In other words, directly using the current limiting link (R f ) and some virtual resistor current limiting methods reduce the transient stability of VSG, while the grid resistance R g It will improve transient stability.

[0084] Combined with the above analysis, the present invention proposes a VSG control strategy based on virtual circuit elements (VCE-VSG), such as Figure 4 As shown in the figure, virtual capacitor and virtual resistor are used to compensate the output voltage and power angle respectively. The virtual capacitor C v The voltage E generated on vc It can compensate the VSG output voltage and further improve the U t Similarly, the virtual resistor R v It can limit the power angle change and play a positive role in current limitation.

[0085] like Figure 5 As shown, the control strategy expression is:

[0086]

[0087] kas and k vs It is a fault judgment switch, which is 1 when a fault occurs, otherwise it is 0. When a fault occurs, the virtual capacitor is first put into use and supports the voltage. At this time, it is necessary to judge the line current i o Whether it exceeds the preset holding current i h , if i o >i h , then it is considered that R v To limit the active current and slow down the power angle change. v When the suppression capacity reaches its limit, the current is still limited. At this time, the VSG acts as a reactive compensation device and only outputs reactive power to support the PCC voltage.

[0088] When the voltage drop is small and the current limit is not triggered, VCE-VSG can effectively support the PCC voltage, and at the same time, virtual resistance can be used to reduce the active output to maintain the power angle stability; when the grid voltage drops deeply, the current limit is easily triggered, and the voltage support and power angle suppression strategies need to work together, which can increase the grid-side virtual resistance R v The value of the current limiting circle is increased to keep the current at i max And further release the virtual capacitor voltage compensation capability, respectively as follows Figure 6 and Figure 7 In fact, this strategy realizes the redistribution of fault current during current limiting, that is, while maintaining i o＝ i max Under the premise of reducing active current and increasing reactive current, the proposed method has better stability than virtual capacitor and virtual resistor methods.

[0089] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0090] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks 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 produce 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.

[0091] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0092] 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.

[0093] Although the preferred embodiments of the present invention 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 that fall within the scope of the present invention.

[0094] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An improved VSG control method suitable for transient power angle suppression and voltage support, characterized in that: include, Obtain the power angle reference value δ* and the internal potential reference value E*; wherein the power angle reference value δ* is determined according to the active power given value P0, the active electromagnetic power P e , the angular frequency rated value ω0 is obtained by the Pf control link; the internal potential reference value E* is based on the reactive power given value Q0, the reactive electromagnetic power Q e , the voltage rating E0 is obtained by using the QU control link; If it is determined that a voltage sag fault occurs in the power grid, at least one of Scheme 1 and Scheme 2 is adopted; wherein, Scheme 1 includes inputting a virtual resistance feedback link into the Pf control link to achieve power angle compensation; Scheme 2 includes inputting a virtual capacitor feedback link into the QU control link to achieve output voltage compensation.

2. The method according to claim 1, characterized in that: The Pf control link includes: Get the active power given value P0, active electromagnetic power P e , respectively input into the positive input terminal and the negative input terminal of the first adder; The output end of the first adder is connected to the positive input end of the second adder, and the output end of the damping link is connected to the negative input end of the second adder; The output end of the second adder passes through a feedback link having an inertia damping system to obtain a change in angular frequency, and the change in angular frequency is also sent to the input end of the damping link; The change in angular frequency and the rated angular frequency value ω0 are connected to the third adder for addition, and then pass through the first integrator to obtain a power angle reference value δ*.

3. The method according to claim 1, characterized in that: The QU control link includes: Get the reactive power given value Q0, reactive electromagnetic power Q e , respectively input into the positive input terminal and the negative input terminal of the fourth adder; Get the voltage rating E0 and the grid connection point voltage U t , respectively input into the positive input terminal and the negative input terminal of the fifth adder; The output ends of the fourth adder and the fifth adder are respectively subjected to the reactive coefficient k q , voltage coefficient k u The output is amplified and connected to a sixth adder for addition operation and then sent to a second integrator; The output of the second integrator and the voltage rated value E0 are connected to a seventh adder for addition operation to obtain an internal potential reference value E*.

4. The method according to claim 1, characterized in that: The expression of the virtual resistance feedback link is: Among them, G(R V ) is the transfer function of the virtual resistor feedback link; U t is the grid voltage, U g is the grid side voltage, δ is the power angle, X g is the grid side inductance, R v is a virtual resistor.

5. The method according to claim 1, characterized in that: The expression of the virtual capacitor feedback link is: G(C V )=ω0Z f C v U t Among them, G(C V ) is the transfer function of the virtual capacitor feedback link; ω0 is the rated value of the angular frequency, Z f is the VSG outlet impedance, C v is the virtual capacitor, U t is the grid connection point voltage.

6. An improved VSG control system suitable for transient power angle suppression and voltage support, characterized in that: include, Pf control link is used to control the active power given value P0 and active electromagnetic power P e , the rated value of angular frequency ω0 is used to obtain the reference value of power angle δ*; The QU control link is used to control the reactive power given value Q0 and reactive electromagnetic power Q e , grid connection point voltage U t , the voltage rated value E0 is used to obtain the internal potential reference value E*; A reference voltage generation module, used to generate a reference voltage for VSG control according to a power angle reference value δ* and an internal potential reference value E*; The virtual resistance feedback link is used to select and connect to the Pf control link to achieve power angle compensation when a voltage sag fault occurs in the power grid; and The virtual capacitor feedback link is used to be selected to connect to the QU control link to achieve output voltage compensation when a voltage sag fault occurs in the power grid.

7. The system according to claim 6, characterized in that: The Pf control link includes: Get the active power given value P0, active electromagnetic power P e , respectively input into the positive input terminal and the negative input terminal of the first adder; The output end of the first adder is connected to the positive input end of the second adder, and the output end of the damping link is connected to the negative input end of the second adder; The output end of the second adder passes through a feedback link having an inertia damping system to obtain a change in angular frequency, and the change in angular frequency is also sent to the input end of the damping link; The change in angular frequency and the rated angular frequency value ω0 are connected to the third adder for addition, and then pass through the first integrator to obtain a power angle reference value δ*.

8. The system according to claim 6, characterized in that: The QU control link includes: Get reactive power given value Q0, reactive electromagnetic power Q e , respectively input into the positive input terminal and the negative input terminal of the fourth adder; Get the voltage rating E0 and the grid connection point voltage U t , respectively input into the positive input terminal and the negative input terminal of the fifth adder; The output ends of the fourth adder and the fifth adder are respectively subjected to the reactive coefficient k q , voltage coefficient k u The output is amplified and connected to a sixth adder for addition operation and then sent to a second integrator; The output of the second integrator and the voltage rated value E0 are connected to a seventh adder for addition operation to obtain an internal potential reference value E*.

9. The system according to claim 6, characterized in that: The expression of the virtual resistance feedback link is: Among them, G(R V ) is the transfer function of the virtual resistor feedback link; U t is the grid voltage, U g is the grid side voltage, δ is the power angle, X g is the grid side inductance, R v is a virtual resistor.

10. The system according to claim 6, characterized in that: The expression of the virtual capacitor feedback link is: G(C V )=ω0Z f C v U t Among them, G(C V ) is the transfer function of the virtual capacitor feedback link; ω0 is the rated value of the angular frequency, Z f is the VSG outlet impedance, C v is the virtual capacitor, U t is the grid connection point voltage.

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