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

Abstract

The application discloses an improved VSG control method suitable for transient power angle suppression and voltage support, and the method comprises the following steps: obtaining a power angle reference value δ* and an internal potential reference value E*, and generating a reference voltage of VSG control; wherein the power angle reference value δ* is obtained by using a P-f control link according to an active power given value P e 0, an active electromagnetic power P e 0 and an angular frequency rated value ω0; the internal potential reference value E* is obtained by using a Q-U control link according to a reactive power given value Q0, a reactive electromagnetic power Q t 0 and a voltage rated value E0; if a voltage sag fault occurs in a power grid, at least one of scheme one and scheme two is used; wherein the scheme one comprises inputting a virtual resistance feedback link to the P-f control link to realize power angle compensation; the scheme two comprises inputting a virtual capacitor feedback link to the Q-U control link to realize output voltage compensation. The application can suppress power angle divergence and improve voltage support capability under the condition of considering fault current limiting.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation control, and relates to a fault ride-through strategy suitable for large disturbances in hydrogen production systems, and particularly to an improved VSG control method suitable for transient power angle suppression and voltage support. Background Technology

[0002] Driven by the decarbonization needs of industries such as power, energy, chemicals, and metallurgy, many countries have listed green hydrogen as an energy strategic direction. To ensure that hydrogen production systems do not rely on external power grids, flexible planning can be carried out based on wind and solar resources and the spatial distribution of hydrogen demand, using grid-type virtual synchronous generators (VSGs) to construct grid voltage and frequency. When simulating the operating characteristics of synchronous generators, VSGs also encounter transient stability problems with large disturbances, among which voltage stability and power angle stability are the most prominent.

[0003] Regarding transient voltage stability, traditional QU control reduces the internal potential of the VSG during transients, thus decreasing its transient stability. However, current research mostly focuses on parameter effects, with fewer strategies for voltage stabilization. Typically, a virtual capacitor is used to output reactive power for support, which can be defined as virtual capacitor control (VC-VSG). The continuous change in the power angle is constrained by the difference between the reference and actual active power values. To address the power angle divergence problem, most research focuses on reducing the power difference, with virtual resistance control (VR-VSG) being an important method. Furthermore, adding transient damping or modifying the damping coefficient in the active power control loop can simultaneously improve synchronization stability and power angle stability. However, it is worth noting that during fault evolution, the change in power angle lags behind the voltage, and current research generally neglects the impact of the QU control loop or current limiting on the VSG. Summary of the Invention

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

[0005] To achieve the above objectives, the solution of the present invention is:

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

[0007] The power angle reference value δ* and the internal electromotive force reference value E* are obtained to generate the reference voltage for VSG control; wherein, the power angle reference value δ* is based on the active power setpoint P0 and the active electromagnetic power P e The rated angular frequency ω0 is obtained using a Pf control loop; the internal electromotive force reference value E* is based on the reactive power setpoint Q0 and the reactive electromagnetic power Q. e Grid connection point voltage U tThe rated voltage E0 is obtained using a QU control loop;

[0008] If a voltage dip fault is detected in the power grid, at least one of Scheme 1 or Scheme 2 shall be adopted. Scheme 1 includes adding a virtual resistance feedback loop to the Pf control loop to achieve power angle compensation; Scheme 2 includes adding a virtual capacitor feedback loop to the QU control loop to achieve output voltage compensation.

[0009] This includes obtaining the power angle reference value δ* and the internal potential reference value E*, and generating the reference voltage for VSG control, including...

[0010]

[0011] In the formula, ω0 is the rated angular frequency, t is time, and E* is the reference voltage amplitude, which generates the reference voltage for VSG control.

[0012] The Pf control loop includes,

[0013] Obtain the active power setpoint P0 and the active electromagnetic power P e The positive and negative inputs of the first adder are respectively input to the positive and negative input terminals.

[0014] The output of the first adder is connected to the positive input of the second adder, and the output of the damping circuit is connected to the negative input of the second adder.

[0015] The output of the second adder passes through a feedback loop with an inertial damping system to obtain the change in angular frequency, which is then fed into the input of the damping loop.

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

[0017] The expression for the Pf control loop is as follows:

[0018]

[0019] The QU control component includes,

[0020] Obtain the reactive power setpoint Q0 and the reactive electromagnetic power Q. e Input the positive and negative input terminals of the fourth adder respectively;

[0021] Obtain the rated voltage E0 and the grid connection point voltage U t Input the positive and negative input terminals of the fifth adder respectively;

[0022] The outputs of the fourth and fifth adders are respectively connected to the reactive power coefficient k.q Voltage coefficient k u The amplified output is connected to the sixth adder for addition, and then fed into the second integrator;

[0023] The output of the second integrator is connected to the voltage rating E0 and then to the seventh adder for addition to obtain the internal potential reference value E*.

[0024] The expression for the QU control loop is as follows:

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

[0026] The expression for the virtual resistance feedback loop is as follows:

[0027]

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

[0029] The expression for the virtual capacitor feedback loop is as follows:

[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 loop; ω0 is the rated angular frequency, Z f For the VSG output-side impedance, C v For virtual capacitance, U t This is the voltage at the grid connection point.

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

[0033] The Pf control loop is used to determine the active power setpoint P0 and the active electromagnetic power P. e The reference value of the power angle δ* is obtained from the rated angular frequency ω0;

[0034] The QU control loop is used to determine the reactive power setpoint Q0 and the reactive electromagnetic power Q. e Grid connection point voltage Ut The internal potential reference value E* is obtained from the voltage rating value E0;

[0035] The reference voltage generation module is used to generate a reference voltage for VSG control based on the power angle reference value δ* and the internal potential reference value E*.

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

[0037] The virtual capacitor feedback loop is used to select and connect to the QU control loop when a voltage dip fault occurs in the power grid, so as to achieve output voltage compensation.

[0038] The Pf control loop includes,

[0039] Obtain the active power setpoint P0 and the active electromagnetic power P e The positive and negative inputs of the first adder are respectively input to the positive and negative input terminals.

[0040] The output of the first adder is connected to the positive input of the second adder, and the output of the damping circuit is connected to the negative input of the second adder.

[0041] The output of the second adder passes through a feedback loop with an inertial damping system to obtain the change in angular frequency, which is then fed into the input of the damping loop.

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

[0043] The QU control component includes,

[0044] Obtain the reactive power setpoint Q0 and the reactive electromagnetic power Q. e Input the positive and negative input terminals of the fourth adder respectively;

[0045] Obtain the rated voltage E0 and the grid connection point voltage U t Input the positive and negative input terminals of the fifth adder respectively;

[0046] The outputs of the fourth and fifth adders are respectively connected to the reactive power coefficient k. q Voltage coefficient k u The amplified output is connected to the sixth adder for addition, and then fed into the second integrator;

[0047] The output of the second integrator is connected to the voltage rating E0 and then to the seventh adder for addition to obtain the internal potential reference value E*.

[0048] The expression for the virtual resistance feedback loop is as follows:

[0049]

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

[0051] The expression for the virtual capacitor feedback loop is as follows:

[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 loop; ω0 is the rated angular frequency, Z f For the VSG output-side impedance, C v For virtual capacitance, U t This is the voltage at the grid connection point.

[0054] By adopting the above scheme, this invention reveals the transient characteristics of different QU control structures under both current-limited and current-limited conditions, demonstrating the adverse effects of current-limiting circuits on power angle stability. Subsequently, by establishing a VSG equivalent circuit model considering fault current limiting, this invention provides a representation method for different QU control structures on the phasor diagram, revealing that effective voltage support is beneficial to improving transient stability. Furthermore, it proposes two transient control methods: improving the QU control circuit using virtual capacitance and improving the Pf control circuit using virtual resistance, to simultaneously solve the voltage support and power angle stability problems, thereby reducing the risk of fault instability. Attached Figure Description

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

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

[0057] (a) represents the case without flow restriction, and (b) represents the case with flow restriction.

[0058] Figure 3 These are voltage equivalent curves under different parameters of this invention;

[0059] Figure 4 This is the equivalent circuit diagram of the strategy proposed in this invention;

[0060] Figure 5 This is a diagram of the control strategy proposed in this invention;

[0061] Among them, (a) is the virtual resistance improved Pf control loop, and (b) is the virtual capacitance improved QU control loop;

[0062] Figure 6 The figure shows the experimental results of different control strategies under the condition of grid voltage drop and no current limiting.

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

[0064] Figure 7 The figure shows the experimental results of different control strategies under the condition of grid voltage drop and current limiting;

[0065] Wherein, (a) is the traditional VSG, and (b) is the control strategy of the present invention (VCE-VSG). Detailed Implementation

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

[0067] Firstly, as Figure 1 The diagram shown is the circuit topology of the virtual synchronous generator grid-connected system to which this invention applies. The DC power supply is the hydrogen production system's input side, and the DC power is inverted by a VSC and connected to the AC grid. E,U g These are the internal potential of the VSG and the grid voltage, respectively. U t and i o These are the voltage and current at the grid connection point. L f ,R f ,L g and R g This indicates the VSG output-side inductance and resistance, and the grid-side inductance and resistance.

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

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

[0070] Where Q0 and E0 are the reactive power setpoint and voltage reference value, respectively. In the QU controller, the virtual electromotive force E is obtained by integrating the weighted average of the reactive power deviation and voltage amplitude deviation, k q and k u These represent the reactive power coefficient and voltage coefficient, respectively, and both are ≥0. When kq When k = 0, the QU controller operates under constant voltage control; when k u When k = 0, it is constant reactive power control; when k q *k u When the value is ≠0, it is a reactive droop control.

[0071] To meet the current stress limitation of power electronic devices, this embodiment adopts a dq-axis constant amplitude current limiter, i max i is the maximum current that the inverter can accommodate. o * is the current command generated by the voltage loop, because i o ≤i max Therefore, the grid connection point voltage U t The terminal B will never exceed the grid voltage U. g Centered on Z g *i max The range of a circle with radius is called the current limiting circle, such as... Figure 2 As shown, the expression for the output current under current-limited conditions can be written as:

[0072]

[0073] in:

[0074]

[0075] Based on the vector relationship, we can obtain:

[0076]

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

[0078]

[0079] Where μ=(1-ρ)*X g / ρ.

[0080] U t The voltage equivalent curve can reflect the reactive voltage stability characteristics during a fault. The transient stability margin increases as ρ decreases, and the power angle change changes from divergent to convergent. Constant reactive power control (ρ=1) has the lowest transient stability margin, while constant voltage control (ρ=0) has the best stability. The stability of reactive power droop control depends on the value of ρ. Constant voltage control can keep the grid connection point voltage at the rated value when the voltage changes slightly, and at the same time, it can make the VSG output the maximum current to support the grid connection point voltage as much as possible when the voltage change is large. Constant reactive power control cannot reliably support U t However, reactive voltage droop control is highly dependent on the ρ value.

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

[0082]

[0083] From the above formula, we can calculate that as R... f Increase, P e Decreasing this will result in the maximum adjustment range δ of the power angle curve. mar As it gradually decreases, the transient stability margin continuously declines, and there is even a risk of work angle divergence. And R... g With R f The opposite effect occurs as R... g Increase, P e Increase, δ mar The increased range of variation leads to faster convergence of the power angle and improved transient stability. In other words, directly using a current-limiting element (R... f The use of virtual resistors for current limiting reduces the transient stability of the VSG, while the grid resistance R... g It will improve transient stability.

[0084] Based on the above analysis, this invention proposes a VSG control strategy based on virtual circuit elements (VCE-VSG), such as... Figure 4 As shown, virtual capacitors and virtual resistors are used to compensate for the output voltage and power angle, respectively. The virtual capacitor C v The voltage E generated on vc It can compensate for the VSG output voltage, further improving the performance of U. t The supporting capacity. Similarly, the virtual resistance R v It can limit changes in the power angle and play a positive role in current limiting.

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

[0086]

[0087] kas and k vs This is a fault detection switch; it is 1 when a fault occurs and 0 otherwise. When a fault occurs, the virtual capacitor is activated first to support the voltage. At this time, it is necessary to determine the line current i. o Does it exceed the preset holding current i? h , if i o >i h Then it is believed that R needs to be invested. v To limit active current and mitigate changes in power angle. When R v When the suppression capability reaches its limit, it still limits the current. At this time, the VSG acts as a reactive power compensation device, only outputting reactive power to support the PCC voltage.

[0088] When the voltage drop is small and does not trigger current limiting, VCE-VSG can effectively support the PCC voltage. Simultaneously, a virtual resistor can be used to reduce active power output and maintain a stable power angle. When the grid voltage drops significantly, current limiting is easily triggered, and voltage support and power angle suppression strategies need to work together. In this case, the grid-side virtual resistor R can be increased. v The value of i increases the radius of the current limiting circle, thus keeping the current at i max And further release the virtual capacitor voltage compensation capability, respectively as follows: Figure 6 and Figure 7 As shown. In fact, this strategy achieves fault current redistribution 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 demonstrates superior stability compared to virtual capacitor and virtual resistor methods.

[0089] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0090] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. 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 illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0091] 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.

[0092] 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.

[0093] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0094] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends 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 based on the active power given value P0 and the active electromagnetic power P e The rated angular frequency ω0 is obtained using a Pf control loop; the internal electromotive force reference value E* is based on the reactive power setpoint Q0 and the reactive electromagnetic power Q. e The rated voltage E0 is obtained using a QU control loop; If a voltage dip fault is detected in the power grid, at least one of Scheme 1 or Scheme 2 shall be adopted. Scheme 1 includes adding a virtual resistance feedback loop to the Pf control loop to achieve power angle compensation; Scheme 2 includes adding a virtual capacitor feedback loop to the QU control loop to achieve output voltage compensation. The expression for the virtual resistance feedback loop is: ， Among them, G(R) V U is the transfer function of the virtual resistance feedback loop; t U is the grid connection point voltage. g The grid-side voltage is δ, the power angle is X. g R is the grid-side inductance. v For virtual resistance; The expression for the virtual capacitor feedback loop is: ， Among them, G(C V ) is the transfer function of the virtual capacitor feedback loop; ω0 is the rated angular frequency, Z f For the VSG output-side impedance, C v For virtual capacitance, U t This refers to the voltage at the grid connection point. When a fault occurs, the virtual capacitor is the first to engage and support the voltage. At this time, it is necessary to determine the line current i. o Does it exceed the preset holding current i? h , if i o >i h Then it is believed that R needs to be invested. v This is to limit the active current and slow down the change in the power angle.

2. The method as described in claim 1, characterized in that: The Pf control loop includes: Obtain the active power setpoint P0 and the active electromagnetic power P e The positive and negative inputs of the first adder are respectively input to the positive and negative input terminals. The output of the first adder is connected to the positive input of the second adder, and the output of the damping circuit is connected to the negative input of the second adder. The output of the second adder passes through a feedback loop with an inertial damping system to obtain the change in angular frequency, which is then fed into the input of the damping loop. The change in angular frequency and the rated angular frequency ω0 are connected to the third adder for addition, and then pass through the first integrator to obtain the power angle reference value δ*.

3. The method as described in claim 1, characterized in that: The QU control mechanism includes: Obtain the reactive power setpoint Q0 and the reactive electromagnetic power Q. e Input the positive and negative input terminals of the fourth adder respectively; Obtain the rated voltage E0 and the grid connection point voltage U t Input the positive and negative input terminals of the fifth adder respectively; The outputs of the fourth and fifth adders are respectively connected to the reactive power coefficient k. q Voltage coefficient k u The amplified output is connected to the sixth adder for addition, and then fed into the second integrator; The output of the second integrator is connected to the voltage rating E0 and then to the seventh adder for addition to obtain the internal potential reference value E*.

4. An improved VSG control system suitable for transient power angle suppression and voltage support, characterized in that: include, The Pf control loop is used to determine the active power setpoint P0 and the active electromagnetic power P. e The reference value of the power angle δ* is obtained from the rated angular frequency ω0; The QU control loop is used to determine the reactive power setpoint Q0 and the reactive electromagnetic power Q. e Grid connection point voltage U t The internal potential reference value E* is obtained from the voltage rating value E0; The reference voltage generation module is used to generate a reference voltage for VSG control based on the power angle reference value δ* and the internal potential reference value E*. The virtual resistance feedback loop is used to select and connect to the Pf control loop when a voltage sag fault occurs in the power grid, thereby achieving power angle compensation; and, The virtual capacitor feedback loop is used to select and connect to the QU control loop when a voltage dip fault occurs in the power grid, so as to achieve output voltage compensation. The expression for the virtual resistance feedback loop is: ， Among them, G(R) V U is the transfer function of the virtual resistance feedback loop; t U is the grid connection point voltage. g The grid-side voltage is δ, the power angle is X. g R is the grid-side inductance. v For virtual resistance; The expression for the virtual capacitor feedback loop is: ， Among them, G(C V ) is the transfer function of the virtual capacitor feedback loop; ω0 is the rated angular frequency, Z f For the VSG output-side impedance, C v For virtual capacitance, U t This refers to the voltage at the grid connection point. When a fault occurs, the virtual capacitor is the first to engage and support the voltage. At this time, it is necessary to determine the line current i. o Does it exceed the preset holding current i? h , if i o >i h Then it is believed that R needs to be invested. v This is to limit the active current and slow down the change in the power angle.

5. The system as described in claim 4, characterized in that: The Pf control loop includes: Obtain the active power setpoint P0 and the active electromagnetic power P. e The positive and negative inputs of the first adder are respectively input to the positive and negative input terminals. The output of the first adder is connected to the positive input of the second adder, and the output of the damping circuit is connected to the negative input of the second adder. The output of the second adder passes through a feedback loop with an inertial damping system to obtain the change in angular frequency, which is then fed into the input of the damping loop. The change in angular frequency and the rated angular frequency ω0 are connected to the third adder for addition, and then pass through the first integrator to obtain the power angle reference value δ*.

6. The system as described in claim 4, characterized in that: The QU control mechanism includes: Obtain the reactive power setpoint Q0 and the reactive electromagnetic power Q. e Input the positive and negative input terminals of the fourth adder respectively; Obtain the rated voltage E0 and the grid connection point voltage U t Input the positive and negative input terminals of the fifth adder respectively; The outputs of the fourth and fifth adders are respectively connected to the reactive power coefficient k. q Voltage coefficient k u The amplified output is connected to the sixth adder for addition, and then fed into the second integrator; The output of the second integrator is connected to the voltage rating E0 and then to the seventh adder for addition to obtain the internal potential reference value E*.

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