Virtual synchronous machine based on extended power transmission module capable of resisting grid side frequency fluctuation

Abstract

The application discloses a virtual synchronous machine based on an extended power transmission module and capable of resisting frequency fluctuation of a grid side, comprising an instantaneous power calculation module, an active power control module, a reactive power control module, a voltage generation module and an extended power transmission module; the voltage generation module is used for determining a reference value of an output voltage of the virtual synchronous machine according to a reference value of a phase angle of the output voltage of the virtual synchronous machine and a reference value of an amplitude of the output voltage of the virtual synchronous machine; the extended power transmission module is connected to an output current of the virtual synchronous machine and is used for correcting the output voltage of the virtual synchronous machine so as to improve the damping characteristic of the virtual synchronous machine to frequency disturbance of the grid side. The application can effectively solve the problem of transient oscillation caused by the fact that various control methods of the existing virtual synchronous machine cannot resist frequency disturbance of the grid.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter and virtual synchronous machine control technology, and in particular to a virtual synchronous machine based on an extended power transmission module that can resist grid-side frequency fluctuations. Background Technology

[0002] With the rapid development of distributed power generation, its proportion in the power grid has also increased rapidly. However, this has brought many challenges, especially the reduction in the inertia of the power system, which leads to excessive maximum frequency deviation during power system transient processes, disrupting the frequency stability of the power grid. To enable distributed energy systems to have the same inertia as traditional generators, Virtual Synchronous Generator (VSG) technology has emerged. By incorporating the electromechanical transient equations of synchronous generators into the control of converters, the converters not only possess voltage and frequency regulation characteristics but also provide inertia and damping for the power grid, making it an ideal way to connect new energy power generation to the grid.

[0003] When power commands change abruptly, traditional VSGs exhibit transient oscillations in active power and output frequency. Numerous existing VSG control improvement methods can mitigate the transient power response characteristics of traditional VSGs under power command changes. However, none of these methods address the VSG output power oscillations induced by grid frequency transients and fluctuations; moreover, existing VSG control improvement methods may actually exacerbate the VSG active power oscillation problem caused by grid frequency disturbances. Summary of the Invention

[0004] This invention provides a virtual synchronous machine based on an extended power transmission module that can resist grid-side frequency fluctuations. It can improve the damping characteristics of the virtual synchronous machine to grid-side frequency disturbances and effectively solve the problem of transient oscillation caused by grid frequency disturbances caused by the inability of various control methods of existing virtual synchronous machines to resist grid frequency disturbances.

[0005] This invention provides a virtual synchronous machine based on an extended power transmission module that can withstand grid-side frequency fluctuations. The virtual synchronous machine includes: an instantaneous power calculation module, an active power control module, a reactive power control module, a voltage generation module, and an extended power transmission module. The instantaneous power calculation module receives the output voltage and output current of the virtual synchronous machine and is used to determine the output values ​​of the active and reactive power of the virtual synchronous machine based on these values. The active power control module controls the output power of the virtual synchronous machine based on a reference value and the feedback output value of the virtual synchronous machine's active power. The active power output is controlled to obtain a reference value for the phase angle of the virtual synchronous machine's output voltage. The reactive power control module controls the reactive power output of the virtual synchronous machine based on the reference value of the virtual synchronous machine's reactive power and the feedback output value of the virtual synchronous machine's reactive power to obtain a reference value for the amplitude of the virtual synchronous machine's output voltage. The voltage generation module determines the reference value of the virtual synchronous machine's output voltage based on the reference values ​​of the phase angle and amplitude of the virtual synchronous machine's output voltage. The extended power transmission module connects to the output current of the virtual synchronous machine to correct the output voltage of the virtual synchronous machine, thereby improving the damping characteristics of the virtual synchronous machine against grid-side frequency disturbances.

[0006] The technical solution provided by this invention realizes the extended power transmission model of the virtual synchronous machine by adding an extended power transmission module, thereby increasing the damping characteristics of the virtual synchronous machine to grid-side frequency disturbances, and thus effectively solving the problem of power oscillation of the virtual synchronous machine caused by grid frequency disturbances that existing methods cannot resist.

[0007] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 This is a system structure diagram of a virtual synchronous machine accessing the power grid provided by an embodiment of the present invention;

[0010] Figure 2 This is a power transmission equivalent model structure diagram of a virtual synchronous machine provided in an embodiment of the present invention;

[0011] Figure 3 This is a control block diagram of a virtual synchronizer provided by related technologies;

[0012] Figure 4 This invention provides a Bode diagram of a conventional VSG system.

[0013] Figure 5 This is a schematic diagram of a virtual synchronous machine based on an extended power transmission module provided in an embodiment of the present invention;

[0014] Figure 6 This is a schematic diagram of the denominator of the transfer function of an extended power transmission module provided in an embodiment of the present invention;

[0015] Figure 7 This is a control block diagram of a virtual synchronous machine extended power transmission model implemented based on the extended power transmission module provided in an embodiment of the present invention;

[0016] Figure 8 This is a Bode diagram of an extended portion provided by the present invention;

[0017] Figure 9 This is a comparison diagram of the transient active power output of a traditional VSG and a VSG system with an added extended power transmission module under power grid disturbances, provided by the present invention.

[0018] Figure 10 This is a comparison chart of the response of the active power output values ​​of a traditional VSG and the VSG system provided by this invention when the active power reference value of a VSG suddenly changes to 15KW according to an embodiment of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0020] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0021] Figure 1 This is a system structure diagram of a virtual synchronous machine accessing the power grid provided by an embodiment of the present invention; as shown below. Figure 1 As shown, the virtual synchronous machine intersects with the power grid at the point of common coupling (PCC), i.e., the grid connection point; the PCC serves as the connection point for nonlinear loads. Here, Udc is the DC-side voltage of the virtual synchronous machine under virtual synchronous machine control. In virtual synchronous machine control mode, it needs to be combined with energy storage equipment to maintain DC-side voltage stability and can be considered a constant value; L f and C f This is the output filter of the VSG, where U is the output voltage of the virtual synchronous machine, i1 represents the output current of the grid-side converter, i2 represents the current injected into the grid, and L... g R is the equivalent inductance of the grid-side line. g This is the equivalent resistance of the power grid line.

[0022] Figure 2 This is a power transmission equivalent model structure diagram of a virtual synchronous machine provided in an embodiment of the present invention, such as... Figure 2 As shown, U ref L represents the reference value for the output voltage of the virtual synchronous machine. g R is the equivalent inductance of the grid-side line. g U is the equivalent resistance of the grid-side line. g Let be the grid voltage. Based on the power transfer model of the virtual synchronous machine, the following relationship can be written:

[0023]

[0024] Among them, U refa U represents the reference value of the A-phase output voltage of the VSG. refb U represents the reference value of the B-phase output voltage of the VSG. refc U represents the reference value of the C-phase output voltage of the VSG. ga U represents the A-phase voltage of the power grid. gb U represents the B-phase voltage of the power grid. gc Represents the C-phase voltage of the power grid, R g L is the equivalent resistance of the grid-side line. g i is the equivalent inductance of the grid-side line. a i represents the current in phase A of the power grid. b Indicates the B-phase grid current, i c This represents the C-phase grid current.

[0025] Performing dq transformation and Laplace transform on the above equation, the current expression under the dq axis is obtained as follows:

[0026]

[0027] Among them, i di represents the component of the grid current on the d-axis. q U represents the q-axis component of the grid current. gd U represents the component of the grid voltage on the d-axis. gq U represents the q-axis component of the grid voltage, where ω0 is the reference angular frequency. refd U represents the d-axis component of the VSG's output voltage reference value. refq R represents the q-axis component of the VSG's output voltage reference value. g L is the equivalent resistance of the grid-side line. g This is the equivalent inductance of the power grid side line.

[0028] Ignoring line resistance and taking s = 0, we can obtain the static expression for fully decoupled power transfer:

[0029]

[0030] Where ΔP represents the output value of the VSG active power, and U represents the output voltage of the virtual synchronous machine. g X represents the grid-side voltage. g The equivalent line impedance between the virtual synchronous machine and the power grid is represented by δ, where δ represents the power angle.

[0031] Figure 3 This is a control block diagram of a virtual synchronizer provided by related technologies, for reference. Figure 3 ΔP ref The reference value for the active power of the virtual synchronous machine is represented by ΔP, and the output value for the active power of the virtual synchronous machine is represented by ΔP. Let Δω represent the transfer function of the integrator. g This indicates the angular frequency of the mesh side.

[0032] Where G1 and G2 represent the transfer functions of the power transfer models of the controller and VSG, respectively, and their expressions are as follows:

[0033]

[0034] Where G1 represents the transfer function of the controller, J represents the virtual inertia coefficient of the virtual synchronizer, ω0 represents the reference angular frequency, s is the Laplace operator, and D... p G2 represents the droop factor, G2 represents the transfer function of the VSG power transfer model, and U represents the output voltage of the virtual synchronous machine. g X represents the grid-side voltage. g This represents the equivalent line impedance between the virtual synchronous machine and the power grid.

[0035] It should be noted that this invention uses the small-signal model analysis method to establish a small-signal model of the virtual synchronous machine system, thereby analyzing the virtual synchronous machine system. Δ represents the small-signal model.

[0036] The expression for the open-loop gain of the active power control loop in the virtual synchronous machine system (hereinafter referred to as the traditional VSG system) provided by related technologies is as follows:

[0037]

[0038] Among them, G op This represents the open-loop gain of the active power control loop in a traditional VSG system.

[0039] The denominator X of the transfer function G2 part in the power transfer model of the VSG basic control loop g It is the equivalent inductance, that is: the actual line impedance X between the VSG and the grid connection point. line The virtual impedance X added to the basic control loop of the VSG v The sum. When choosing a value, in order to reduce the line impedance X... line To mitigate the impact on the power structure and ensure that the equivalent impedance is inductive to achieve better transient characteristics, a relatively large virtual impedance value X is typically used in the basic control loop of the VSG. v0 This makes it much larger than the line impedance. At this point, the effect of the line impedance can be ignored, and X can be used in the transfer function G2 of the power transfer model. v0 Equivalent substitution X g .

[0040] Plot the Bode plot of a traditional VSG based on the expression for the open-loop gain of the active power control loop in a traditional VSG system. Figure 4 This is a Bode diagram of a conventional VSG system provided by the present invention, for reference. Figure 4 On the one hand, the introduction of virtual inertia J can improve the inertia of the virtual synchronous machine and enhance its inertia support for the power grid; on the other hand, in the traditional VSG system transfer function, the inherent integral term introduces a 90-degree phase lag, and as the virtual inertia J increases, the pole of the first-order inertial element moves to the left, causing the amplitude-frequency characteristic to cross the 0dB line at -40dB / dec. This causes the virtual synchronous machine to induce power transient oscillations under power grid frequency fluctuations.

[0041] To address the above issues, this invention proposes an extended power transfer model in the VSG control architecture, which is illustrated in the virtual synchronous machine principle block diagram (…). Figure 5 An extended power transmission module is added to the virtual synchronous machine control block diagram (). Figure 7 The extended power transfer model in ). Figure 5 This is a schematic diagram of a virtual synchronous machine based on an extended power transmission module provided in an embodiment of the present invention. (Refer to...) Figure 5The virtual synchronous machine includes: an instantaneous power calculation module 11, an active power control module 12, a reactive power control module 13, a voltage generation module 14, and an extended power transmission module 15.

[0042] The instantaneous power calculation module 11 is connected to the virtual synchronous machine output voltage u and the virtual synchronous machine output current i2. The instantaneous power calculation module 11 is used to determine the output value P of the active power of the virtual synchronous machine based on the virtual synchronous machine output voltage u and the virtual synchronous machine output current i2. out The output value Q of the virtual synchronous machine's reactive power out .

[0043] The active power control module 12 is used to control the active power reference value P of the virtual synchronous machine. ref The output value P of the virtual synchronous machine with feedback active power out The active power output of the virtual synchronizer is controlled to obtain a reference value θ for the phase angle of the virtual synchronizer output voltage. ref .

[0044] The reactive power control module 13 is used to control the reactive power reference value Q of the virtual synchronous machine. ref The output value Q of the virtual synchronous machine for reactive power feedback. out The reactive power output of the virtual synchronizer is controlled to obtain a reference value U for the output voltage amplitude of the virtual synchronizer. ref .

[0045] Voltage generation module 14 is used to generate voltage based on the reference value θ of the phase angle of the output voltage of the virtual synchronizer. ref Reference value U of the output voltage amplitude of the virtual synchronizer ref Determine the reference value u for the output voltage of the virtual synchronizer. ref .

[0046] The extended power transmission module 15 is connected to the output current of the virtual synchronizer to correct the output voltage of the virtual synchronizer, thereby improving the damping characteristics of the virtual synchronizer against grid-side frequency disturbances.

[0047] Specifically, the instantaneous power calculation module 11 can employ the traditional product method, the virtual orthogonal vector calculation method, or the integral averaging method. A droop controller can be used to process the output values ​​of active and reactive power to obtain a reference value for the output voltage of the virtual synchronous machine.

[0048] For example, the output values ​​of the active power and reactive power of the virtual synchronous machine can be determined according to the following formulas. In the stationary coordinate system:

[0049]

[0050]

[0051] Among them, P out Q represents the output value of the virtual synchronous machine's active power. out u represents the output value of the reactive power of the virtual synchronous machine. α u represents the component of the virtual synchronous machine output voltage along the α-axis in the stationary coordinate system. β i represents the component of the virtual synchronous machine output voltage along the β-axis in the stationary coordinate system. 2α This represents the component of the virtual synchronous machine output current i2 along the α-axis in the stationary coordinate system. 2β This represents the component of the virtual synchronous machine output current i2 along the β axis in the stationary coordinate system.

[0052] The active power control module 12 can obtain the reference value of the phase angle of the virtual synchronous machine output voltage according to the following formula:

[0053] P ref -P out -D p (ω m -ω0)=Jω0s;

[0054]

[0055] In the formula, P ref P represents a reference value for the active power of the virtual synchronous machine. out D represents the output value of the active power of the virtual synchronous machine. p The droop control coefficient for active power is represented by J, the virtual inertia by s, and the Laplace operator by ω. m The reference angular frequency of the virtual synchronizer is represented by ω0, where ω0 is the rated frequency and θ is the reference angular frequency. ref This represents the reference value for the phase angle of the output voltage of the virtual synchronous machine.

[0056] The reactive power control module 13 can obtain the reference value of the output voltage amplitude of the virtual synchronous machine according to the following formula:

[0057]

[0058] In the formula, Q ref Q represents a reference value for the reactive power of the virtual synchronous machine. out U represents the output value of the reactive power of the virtual synchronous machine. ref The reference value represents the amplitude of the virtual synchronous machine's output voltage, K represents the gain of the integral controller, U0 represents the rated output voltage amplitude, and U... out D represents the sampled value of the output voltage of the virtual synchronous machine. q denoted by droop control coefficient for reactive power, and s denotes the Laplace operator.

[0059] The voltage generation module 14 can determine the reference value of the virtual synchronizer output voltage according to the following formula:

[0060] u refa =U ref sin(θ ref );

[0061]

[0062]

[0063] In the formula, u refa u represents the reference value of the virtual synchronous machine output voltage of phase A. refb u represents the reference value of the output voltage of the virtual synchronous machine in phase B. refc The reference value U represents the output voltage of the virtual synchronous machine in phase C. ref θ represents a reference value indicating the amplitude of the output voltage of the virtual synchronous machine. ref This represents the reference value for the phase angle of the output voltage of the virtual synchronous machine.

[0064] To ensure that the present invention updates the transfer function G2 of the traditional power transfer model to the transfer function G of the extended power transfer model... M Then, the equivalent inductance value in the denominator is compared with X in the traditional VSG. g To maintain consistency, this invention adds X to the denominator of the extended power transfer model. v0 The denominator of the transfer function in the extended power transfer model is denoted as G. Mden Its expression is:

[0065]

[0066] Where τ1 and τ2 are compensation coefficients, s is the Laplace transform operator, a is the pole adjustment parameter, and b is the zero adjustment parameter.

[0067] From the above equation, it can be seen that to ensure the steady-state value of the power transfer model remains unchanged before and after the extension, a = b must be set. For simplicity, we take a = b = 1 here. Thus, the denominator G of the transfer function of the extended power transfer model is... Mden The specific form is as follows:

[0068]

[0069] In summary, the transfer function of the extended power transfer model satisfies the following relationship:

[0070]

[0071] Among them, G MTo extend the transfer function of the power transfer model, τ1 and τ2 are compensation coefficients, and U represents the amplitude of the output voltage of the virtual synchronous machine. g X represents the grid-side voltage. v0 Let represent the initial value of the denominator of the transfer function in the extended power transfer model, and s be the Laplace operator.

[0072] Figure 6 This is a schematic diagram of the denominator of the transfer function of an extended power transmission module provided in an embodiment of the present invention. (Refer to...) Figure 6 To address the power coupling issue caused by the extension of the power transfer model, the 90° phase difference between the d and q axes can be utilized. This can be achieved through coordinate system cross-transformation to extend the power transfer module 15. Specifically, the current command in the αβ stationary coordinate system is transformed to the dq rotating coordinate system. Since the d-axis current reflects the frequency characteristics of the output active power, improving the active transient response of the VSG becomes possible. Therefore, the dq-axis current is multiplied by a coefficient X. v0 Then, an extension 150 is added. At this point, the voltage is the voltage drop generated after adding the extension 150 to the traditional VSG transmission model. After transforming to the αβ stationary coordinate system, it is compensated to the voltage command value u. ref .

[0073] Among them, reference Figure 6 u refα The reference value of the virtual synchronous machine output voltage from the voltage generation module is represented by the α-axis component in the stationary coordinate system, u. refβ The reference value of the virtual synchronous machine output voltage from the voltage generation module is represented by the β-axis component in the stationary coordinate system. This represents the component of the reference value of the output voltage of the virtual synchronous machine after the addition of the extended section, expressed on the α-axis in the stationary coordinate system. This represents the β-axis component of the reference value of the output voltage of the virtual synchronous machine after the addition of the extended part in the stationary coordinate system.

[0074] Assuming that after expanding the power transmission module 15, the cutoff frequency of the VSG system is ω c1 The traditional VSG system at ω c1 The phase at that point can be expressed as The ideal phase margin of the extended VSG system is expressed as PM*. Therefore, the parameters of the extended power transfer module 15 should be derived from the parameters of the traditional VSG system at ω. c1 The phase at the given point and the ideal phase margin are jointly determined. The compensation coefficients τ1 and τ2 should satisfy the following relationship:

[0075]

[0076] Where, ω c1The cutoff frequency of the virtual synchronizer is represented by , and PM* represents the ideal phase margin of the extended virtual synchronizer. This indicates that the traditional virtual synchronizer is at ω c1 The phase at that point.

[0077] The cutoff frequency of a traditional VSG system is 13 rad / s. After extension, since τ1≠τ2, the cutoff frequency of the extended VSG system will decrease. This invention uses ω c1 = 8 rad / s. The phase margin of a traditional VSG at a cutoff frequency of 8 rad / s is 20°. This invention uses a typical second-order system with an optimal damping ratio ξ = 0.707 as a design reference; therefore, the cutoff frequency ω of the extended VSG system is... c1 When the speed is 8 rad / s, the ideal phase margin PM* = 45°. According to the above formula, τ1 is 0.05 and τ2 is 0.3.

[0078] Figure 7 This is a control block diagram of a virtual synchronous machine extended power transmission model implemented based on the extended power transmission module 15, provided by an embodiment of the present invention. (Refer to...) Figure 7 ΔP ref The reference value for the active power of the virtual synchronous machine is represented by ΔP, and the output value for the active power of the virtual synchronous machine is represented by ΔP. Let Δω represent the transfer function of the integrator. g This indicates the angular frequency of the mesh side.

[0079] The expression for the open-loop gain of the active power loop of the virtual synchronous machine based on the extended power transmission module 15 is as follows:

[0080]

[0081] Among them, P loop The open-loop gain of the active power control loop of the VSG system based on the extended power transmission module 15 is represented by J, where J represents the virtual inertia coefficient of the virtual synchronous machine, ω0 represents the reference angular frequency, s is the Laplace operator, and D is the virtual inertia coefficient of the virtual synchronous machine. p U represents the droop factor, and U represents the output voltage of the virtual synchronous machine. g X represents the grid-side voltage. v0 The denominator of the transfer function in the extended power transfer model is represented by τ1 and τ2, which are compensation coefficients.

[0082] Furthermore, the addition of extension 150 can be equivalent to adding a pair of zeros and poles to the loop gain of the virtual synchronous machine system, when At that time, the active power control loop gain P loop =0, therefore For the zero point of the active power control loop gain, when At this time, the active power loop gain approaches infinity, therefore for The poles of the loop gain.

[0083] Furthermore, the parameters of the extension section 150 are simple to set and easy to adjust, without introducing any uncertainties. Moreover, since there are adjustable parameters in both the numerator and denominator of the transfer function of the extension section 150, the frequency support characteristics of the virtual synchronous machine itself can be maintained by adjusting the pole adjustment parameters and the zero adjustment parameters, without introducing nonlinear factors.

[0084] Furthermore, since the pole adjustment parameters and zero adjustment parameters are adjustable, after adding the extension section 150, the loop gain of the virtual synchronous machine can be controlled by adjusting the pole adjustment parameters and zero adjustment parameters, ensuring that the loop gain of the virtual synchronous machine will not decrease. This is beneficial to improving the damping characteristics of the virtual synchronous machine against grid-side frequency disturbances and effectively solving the problem of transient oscillations caused by grid frequency disturbances that cannot be resisted by various existing control methods of virtual synchronous machines.

[0085] Figure 8 This is a Bode diagram of an extended portion provided by the present invention, for reference. Figure 8 The extended section of the extended power transmission module 15 has a large gain in the low-frequency band. The gain is high at the power frequency and low at high frequencies; this can be seen from the phase frequency characteristics, as the extended section replaces the equivalent impedance X in the original denominator. g Therefore, the reciprocal of the extended part has a large phase margin at the power frequency.

[0086] Figure 9 This is a comparison diagram of the transient active power output of a traditional VSG and a VSG system with an added extended power transmission module 15 under grid disturbances, provided by the present invention. Figure 9 As shown in the figure, the dashed line represents the output active power curve of the traditional scheme, i.e., the traditional virtual synchronous machine, while the solid line represents the output active power curve of the scheme of this invention, i.e., the virtual synchronous machine after adding the extended power transmission module 15. When the grid frequency drops by 0.1Hz, compared with the traditional VSG system, the VSG system with the extended power transmission module 15 has no oscillating element in its power response, and the overshoot is only 33%, with a settling time of about 0.8s. Compared with the traditional VSG system, which has an overshoot of 61% and a settling time of 3s, the transient performance is significantly improved. Moreover, since the VSG active power loop has a droop controller to simulate primary frequency regulation, the droop characteristics of the VSG can be kept unchanged before and after the modification.

[0087] Figure 10 This is a comparison chart of the active power output values ​​of a traditional VSG and the VSG system provided by this invention when the active power reference value of a VSG suddenly changes to 15KW, according to an embodiment of this invention. Figure 10 The dashed line in the figure represents the traditional scheme, i.e., the output active power curve corresponding to the traditional virtual synchronous machine. The solid line represents the scheme of this invention, i.e., the output active power curve corresponding to the virtual synchronous machine after adding the extended power transmission module 15. Under grid-connected operation, when the set output active power (i.e., the VSG active power reference value) suddenly changes to 15kW, the output active power curve (i.e., the VSG active power output value) of the traditional VSG exhibits significant oscillations, with an overshoot reaching 61%. It eventually stabilizes at 15kW without steady-state error. Excessive oscillations in output active power pose a significant threat to the safe and stable operation of the virtual synchronous machine, potentially causing it to automatically shut down and disconnect from the grid due to overcurrent, or even damaging the power electronic equipment. After adding the extended power transmission module 15 to the traditional VSG system, the overshoot decreases to 6.7%, the transient characteristics of the VSG system are significantly improved, and power oscillations are effectively suppressed.

[0088] from Figure 9 and Figure 10 It can be seen that by adding an extended power transfer model to the VSG control loop, the damping characteristics of the virtual synchronous machine to grid-side frequency disturbances can be increased. Therefore, this invention can improve the transient power response characteristics of the VSG under power command mutations, just like existing methods, while also solving the problem that existing VSG methods suffer from deteriorated active power oscillations due to grid frequency disturbances.

[0089] Continue to refer to Figure 5 Optionally, the virtual synchronizer based on the extended power transmission module also includes a voltage and current control module 16, which is used to follow the reference value of the output voltage of the virtual synchronizer.

[0090] The virtual synchronous machine based on the extended power transmission module also includes a PWM modulation module 17 and an inverter 18. The PWM modulation module 17 is used to output a chopping signal to drive the inverter.

[0091] The working process of the transient control system of the virtual synchronous machine provided in this embodiment of the invention is as follows: The instantaneous power calculation module 11 determines the output value of the active power and the output value of the reactive power of the virtual synchronous machine based on the output voltage and output current of the virtual synchronous machine. The active power control module 12 controls the output value of the VSG active power output by the instantaneous power calculation module 11 based on the reference value of the VSG active power, so that the output value of the VSG active power tracks the reference value of the VSG active power. The reactive power control loop 13 controls the output value of the instantaneous power calculation module 11 based on the reference value of the VSG reactive power. The output value of the VSG reactive power is controlled so that the output value of the VSG reactive power tracks the reference value of the VSG reactive power. The voltage generation module 14 determines the reference value of the output voltage of the virtual synchronous machine based on the output value of the active power and the output value of the virtual synchronous machine reactive power, and inputs the reference value of the output voltage of the virtual synchronous machine to the voltage and current control module 16. The voltage and current control module 16 controls the output voltage of the virtual synchronous machine according to the reference value of the output voltage of the virtual synchronous machine, so that the output voltage of the virtual synchronous machine always follows the voltage reference value, and outputs the chopping signal to drive the inverter through the PWM modulation module 17.

[0092] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A virtual synchronous machine based on an extended power transmission module that can resist grid-side frequency fluctuations, characterized in that, include: Instantaneous power calculation module, active power control module, reactive power control module, voltage generation module, and extended power transmission module; The instantaneous power calculation module is connected to the output voltage and output current of the virtual synchronous machine. The instantaneous power calculation module is used to determine the output value of the active power and the output value of the reactive power of the virtual synchronous machine based on the output voltage and output current of the virtual synchronous machine. The active power control module is used to control the active power output by the virtual synchronous machine based on the reference value of the active power of the virtual synchronous machine and the feedback output value of the active power of the virtual synchronous machine, so as to obtain the reference value of the phase angle of the output voltage of the virtual synchronous machine. The reactive power control module is used to control the reactive power output of the virtual synchronous machine based on the reactive power reference value of the virtual synchronous machine and the feedback output value of the reactive power of the virtual synchronous machine, so as to obtain the reference value of the output voltage amplitude of the virtual synchronous machine. The voltage generation module is used to determine the reference value of the virtual synchronizer output voltage based on the reference value of the phase angle of the virtual synchronizer output voltage and the reference value of the amplitude of the virtual synchronizer output voltage. The extended power transmission module is connected to the output current of the virtual synchronizer to correct the output voltage of the virtual synchronizer, thereby improving the damping characteristics of the virtual synchronizer to grid-side frequency disturbances. The transfer function of the virtual synchronous machine extended power transmission model implemented by the extended power transmission module satisfies the following relationship: ； in, To extend the transfer function of the power transfer model, and For compensation coefficient, This indicates the amplitude of the output voltage of the virtual synchronous machine. Indicates the grid-side voltage. This represents the initial value of the virtual impedance added to the control loop of the virtual synchronous machine. For the Laplace operator; compensation coefficient and The following relationship should be satisfied: ； in, This indicates the cutoff frequency of the virtual synchronizer. This represents the ideal phase margin of the extended virtual synchronizer. This indicates that traditional virtual synchronization machines are in The phase at that point.

2. The extended power transmission module according to claim 1, characterized in that, The extended power transmission module is implemented in a synchronous rotating coordinate system and is used to correct the output voltage of the virtual synchronous machine based on the extended power transmission module.

3. The virtual synchronizer based on the extended power transmission module according to claim 1, characterized in that, It also includes a voltage and current control module, which is used to follow the reference value of the output voltage of the virtual synchronizer.

4. The virtual synchronizer based on the extended power transmission module according to claim 1, characterized in that, It also includes a PWM modulation module and an inverter, wherein the PWM modulation module is used to output a chopping signal to drive the inverter.

5. The virtual synchronous machine based on the extended power transmission module according to claim 1, characterized in that, The instantaneous power calculation module determines the output values ​​of the active power and reactive power of the virtual synchronous machine according to the following formula: ； ； in, This represents the output value of the virtual synchronous machine's active power. This represents the output value of the reactive power of the virtual synchronous machine. This indicates that the output voltage of the virtual synchronous machine is in the stationary coordinate system. Components of the axis, This indicates that the output voltage of the virtual synchronous machine is in the stationary coordinate system. Components of the axis, Indicates the output current of the virtual synchronous machine In the stationary coordinate system Components of the axis, Indicates the output current of the virtual synchronous machine In the stationary coordinate system The components of the axis.

6. The virtual synchronous machine based on the extended power transmission module according to claim 1, characterized in that, The active power control module obtains the reference value of the output voltage phase angle of the virtual synchronous machine according to the following formula: ； ； In the formula, This represents a reference value for the active power of the virtual synchronous machine. This represents the output value of the virtual synchronous machine's active power. The droop control coefficient represents the active power. Represents virtual inertia. Represents the Laplace operator. This represents the reference angular frequency of the virtual synchronizer. For the rated frequency, This represents the reference value for the phase angle of the output voltage of the virtual synchronous machine.

7. The virtual synchronous machine based on the extended power transmission module according to claim 1, characterized in that, The reactive power control module obtains the reference value of the output voltage amplitude of the virtual synchronous machine according to the following formula: ； In the formula, This represents a reference value for the reactive power of the virtual synchronous machine. This represents the output value of the reactive power of the virtual synchronous machine. A reference value representing the amplitude of the output voltage of the virtual synchronous machine. This indicates the gain of the integral controller. Indicates the rated output voltage amplitude. This represents the sampled value of the output voltage of the virtual synchronous machine. The droop control factor represents reactive power. This represents the Laplace operator.

8. The virtual synchronizer based on the extended power transmission module according to claim 1, characterized in that, The voltage generation module determines the reference value of the virtual synchronizer output voltage according to the following formula: ； ； ； In the formula, This represents the reference value for the output voltage of the virtual synchronous machine in phase A. This represents the reference value for the output voltage of the virtual synchronous machine in phase B. This represents the reference value for the output voltage of the virtual synchronous machine in phase C. A reference value representing the amplitude of the output voltage of the virtual synchronous machine. This represents the reference value for the phase angle of the output voltage of the virtual synchronous machine.

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