Improved virtual synchronous machine control strategy based on function control

Abstract

The invention discloses an improved virtual synchronous generator control strategy based on function control, belongs to the technical field of distributed energy grid-connected converters, and particularly relates to a method for improving the control stability of a virtual synchronous generator based on function control. The method comprises a basic virtual synchronous machine VSG control link, a power angle adaptive function control link, an energy function nonlinear power control link and a power angle compensation link. The basic virtual synchronous machine VSG control link provides a basic control structure; in the power angle adaptive function control link, power angle adaptive adjustment is carried out based on disturbance variation of frequency and voltage, and VSG frequency supporting capacity is provided; the nonlinear power control link of the energy function is used for evaluating the energy distribution and dissipation characteristics of the system, so that more accurate power control is realized; and the power angle compensation link compensates for VSG instability caused by power grid voltage fluctuation.

Description

Technical Field

[0001] The present invention discloses an improved virtual synchronous machine control strategy based on function control, which belongs to the technical field of distributed energy grid-connected converters, and in particular relates to a method for improving the control stability of a virtual synchronous generator based on function control. Background Art

[0002] With the rapid development of renewable energy, distributed energy systems play an increasingly important role in modern power systems. Since the access method of distributed energy usually relies on power electronic devices such as inverters to connect to the grid and regulate electricity, how to ensure the stability and safety of these distributed energy systems has become one of the important issues in current power system research.

[0003] As a new type of grid-connected control strategy, the virtual synchronous machine (VSG) aims to improve the stability of distributed energy systems in power networks by simulating the inertia characteristics and regulation capabilities of traditional synchronous generators. However, the current virtual synchronous machine control strategy still faces some challenges in practical applications, especially when the system frequency fluctuates greatly or the load disturbance is severe. The existing control methods may have problems such as response lag and poor stability. These problems will affect the real-time control performance of the virtual synchronous machine, and thus have an adverse effect on the stable operation of the distributed energy system. How to improve its stability and response speed based on the existing virtual synchronous machine control strategy has become a technical problem that needs to be solved urgently.

[0004] The technical solution of the present invention, in view of the above-mentioned problems, proposes an improved virtual synchronous machine control strategy based on function control. By introducing the power angle control function and the nonlinear energy function control, the output of the inverter can be adjusted more accurately and the stability of the virtual synchronous machine under dynamic disturbances can be enhanced. This method can effectively improve the adaptability of the virtual synchronous machine to grid fluctuations and significantly improve the control performance of the distributed energy grid-connected system, ensuring that the power system can still maintain high stability and reliability when facing large-scale renewable energy access. Summary of the invention

[0005] In order to overcome the problems existing in the related art, the present invention discloses and implements an improved virtual synchronous machine control strategy based on function control.

[0006] The technical solution adopted by the present invention is:

[0007] An improved virtual synchronous machine control strategy based on function control, characterized by comprising the following steps:

[0008] Step 1: Establish a traditional virtual synchronous generator VSG control model;

[0009] Step 2: Design the power angle adaptive control function;

[0010] Step 3: Design a nonlinear power control function based on the energy function to perform power angle compensation.

[0011] In step 1, a traditional virtual synchronous generator VSG control model is established, and the specific method is as follows:

[0012] 1) The rotor mechanical equation of primary frequency modulation corresponding to the active power-frequency and reactive power-voltage control links of the virtual synchronous machine VSG is:

[0013]

[0014] In formula (1), J is the virtual moment of inertia, D is the virtual damping coefficient, K p is the active frequency droop coefficient, P m is the virtual mechanical power, P N is the rated input active power, P e is the actual output power, w is the actual output angular frequency, w 0 is the rated input angular frequency, δ is the actual output power angle of VSG, and t is the time;

[0015] 2) The reactive power-voltage droop control equation of the virtual synchronous machine is:

[0016]

[0017] In formula (2), K q is the reactive voltage integral coefficient, K u is the reactive voltage droop coefficient, Q N is the rated input reactive power, Q e is the actual output reactive power, U N is the rated input phase voltage, U is the actual output phase voltage, and E is the VSG output electromotive force amplitude;

[0018] 3) The dynamic characteristic curve of VSG transmitting power to the common coupling point can be expressed by the following formula:

[0019]

[0020] In formula (3), U s is the effective value of the input voltage on the power supply side, R e +jX e is the VSG transmission line impedance, U pcc is the grid coupling point voltage;

[0021] 4) Active power P output by VSG e and reactive power Q e In the two-phase rotating coordinate system, i.e., the dq coordinate system, it can be expressed as:

[0022]

[0023] In formula (4), E d is the d-axis electromotive force, E q is the q-axis electromotive force, i od is the d-axis current, i oq is the q-axis current;

[0024] 5) According to the corresponding parameter relationship between formula (8) and formula (9), we can know that:

[0025]

[0026] 3. In step 2, the power angle adaptive control function is designed, and the specific method is as follows:

[0027] 1) The power angle adaptive control function is:

[0028] δ(t)=δ 0 +f(Δw(t),ΔE(t)) (7);

[0029] In formula (7), δ 0 is the initial output power angle of VSG, f(Δw(t),ΔE(t)) is a nonlinear function, which can perform adaptive adjustment of the power angle based on the disturbance changes of frequency and voltage;

[0030] 2) According to formula (7), the nonlinear regulation function introduced by the VSG power angle adaptive control function takes the angular frequency deviation and voltage deviation as variables, and the deviations are:

[0031]

[0032] In formula (8), w ref and E ref are the reference frequency and reference voltage respectively, w(t) and E(t) are the frequency and voltage currently output by VSG;

[0033] 3) Define the function f(Δw(t),ΔE(t)) as:

[0034]

[0035] In formula (9), k wp and k wi is the proportional and integral gain of the frequency deviation, k up is the proportional gain of the voltage deviation;

[0036] 4) Substituting formula (9) into formula (7), the formula for the dynamic change of power angle is:

[0037]

[0038] 4. In step 3, a nonlinear power control function based on an energy function is designed to perform power angle compensation. The specific method is as follows:

[0039] 1) The nonlinear energy control function is:

[0040]

[0041] V(E d ,E q ,i od ,i oq ) is an energy function, which can be used to evaluate the energy distribution and dissipation characteristics of the system, thereby achieving more accurate power control;

[0042] 2) The energy function introduced in formula (11) is based on the Lyapunov function, so V(E d ,E q ,i od ,i oq ) is non-negative, and the derivative of this function yields:

[0043]

[0044] According to Lyapunov's stability criterion, if Then the Lyapunov function V(E d ,E q ,i od ,i oq ) decreases with time, the system tends to be stable. On the contrary, if Then the function V(E d ,E q ,i od ,i oq ) increases with time, the system is unstable, or is in a boundary stability state, and the energy function V(E d ,E q ,i od ,i oq ) The traditional solution to the unstable state is to increase the system damping or reduce the VSG output power. Increasing the system damping means increasing the virtual damping coefficient D of the VSG or increasing the virtual resistance in the virtual impedance. The present invention chooses to reduce the VSG output power, that is, appropriately reduce the power angle in the adjustment formula of δ(t), so that the output active power and reactive power are reduced, thereby reducing the energy of the system. The present invention chooses to use a mechanical switch to improve formula (10), that is, the power angle;

[0045] 3) When the energy function V(E d ,E q ,i od ,ioq ) is in a stable state, the mechanical switch is at position 0, and when the energy function V(E d ,E q ,i od ,i oq ) is in an unstable state, the mechanical switch is in the power angle compensation position, that is, the actual output power angle δ of VSG is:

[0046]

[0047] In formula (13), k w and are the integral compensation coefficients of the frequency deviation.

[0048] The present invention provides an improved virtual synchronous machine control strategy based on function control, and the technical effects are as follows:

[0049] 1) Introducing the power angle adaptive control function to enhance the frequency support capability of VSG to the power grid;

[0050] 2) Introducing a nonlinear power control function based on energy function to determine the stable state of VSG for power angle compensation;

[0051] 3) Enhance the stability of the virtual synchronous machine under dynamic disturbances and effectively improve the adaptability of the virtual synchronous machine to power grid fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the description, serve to explain the principles of the present disclosure;

[0053] Figure 1 An overall flow chart provided for an embodiment of the present invention;

[0054] Figure 2 An improved virtual synchronous machine control diagram provided by an embodiment of the present invention;

[0055] Figure 3 A schematic diagram of a grid-connected circuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The following is combined with Figures 1 to 3 The present invention is described in detail so that those skilled in the art can better understand the present invention and implement it, but it is not intended to limit the scope of protection of the present application.

[0057] Figure 1 An overall flow chart provided for an embodiment of the present invention;

[0058] Figure 2 The improved virtual synchronous machine control diagram provided by the embodiment of the present invention is established by including the following steps:

[0059] Step 1: Establish a traditional virtual synchronous generator VSG control model;

[0060] Step 2: Design the power angle adaptive control function;

[0061] Step 3: Design a nonlinear power control function based on the energy function to perform power angle compensation.

[0062] In step 1, a traditional virtual synchronous generator VSG control model is established, and the specific method is as follows:

[0063] 1) The rotor mechanical equation of primary frequency modulation corresponding to the active power-frequency and reactive power-voltage control links of the virtual synchronous machine VSG is:

[0064]

[0065] In formula (1), J is the virtual moment of inertia, D is the virtual damping coefficient, K p is the active frequency droop coefficient, P m is the virtual mechanical power, P N is the rated input active power, P e is the actual output power, w is the actual output angular frequency, w 0 is the rated input angular frequency, δ is the actual output power angle of VSG, and t is the time;

[0066] 2) The reactive power-voltage droop control equation of the virtual synchronous machine is:

[0067]

[0068] In formula (2), K q is the reactive voltage integral coefficient, K u is the reactive voltage droop coefficient, Q N is the rated input reactive power, Q e is the actual output reactive power, U N is the rated input phase voltage, U is the actual output phase voltage, and E is the VSG output electromotive force amplitude;

[0069] 3) Figure 3 A schematic diagram of a grid-connected line provided in an embodiment of the present invention, VSG to Figure 3 The dynamic characteristic curve of the power delivered by the common coupling point PCC can be expressed as follows:

[0070]

[0071] In formula (3), U s is the effective value of the input voltage on the power supply side, R e +jX eis the VSG transmission line impedance, U pcc is the grid coupling point voltage;

[0072] 4) Active power P output by VSG e and reactive power Q e In the two-phase rotating coordinate system, i.e., the dq coordinate system, it can be expressed as:

[0073]

[0074] In formula (4), E d is the d-axis electromotive force, E q is the q-axis electromotive force, i od is the d-axis current, i oq is the q-axis current;

[0075] 5) According to the corresponding parameter relationship between formula (8) and formula (9), we can know that:

[0076]

[0077] In step 2, a power angle adaptive control function is designed, and the specific method is as follows:

[0078] 1) The power angle adaptive control function is:

[0079] δ(t)=δ 0 +f(Δw(t),ΔE(t)) (7);

[0080] In formula (7), δ 0 is the initial output power angle of VSG, f(Δw(t),ΔE(t)) is a nonlinear function, which can perform adaptive adjustment of the power angle based on the disturbance changes of frequency and voltage;

[0081] 2) According to formula (7), the nonlinear regulation function introduced by the VSG power angle adaptive control function takes the angular frequency deviation and voltage deviation as variables, and the deviations are:

[0082]

[0083] In formula (8), w ref and E ref are the reference frequency and reference voltage respectively, w(t) and E(t) are the frequency and voltage currently output by VSG;

[0084] 3) Define the function f(Δw(t),ΔE(t)) as:

[0085]

[0086] In formula (9), k wp and k wiis the proportional and integral gain of the frequency deviation, k up is the proportional gain of the voltage deviation;

[0087] 4) Substituting formula (9) into formula (7), the formula for the dynamic change of power angle is:

[0088]

[0089] In step 3, a nonlinear power control function based on an energy function is designed to perform power angle compensation. The specific method is as follows:

[0090] 1) The nonlinear energy control function is:

[0091]

[0092] V(E d ,E q ,i od ,i oq ) is an energy function, which can be used to evaluate the energy distribution and dissipation characteristics of the system, thereby achieving more accurate power control;

[0093] 2) The energy function introduced in formula (11) is based on the Lyapunov function, so V(E d ,E q ,i od ,i oq ) is non-negative, and the derivative of this function yields:

[0094]

[0095] According to Lyapunov's stability criterion, if Then the Lyapunov function V(E d ,E q ,i od ,i oq ) decreases with time, the system tends to be stable. On the contrary, if Then the function V(E d ,E q ,i od ,i oq ) increases with time, the system is unstable, or is in a boundary stability state, and the energy function V(E d ,E q ,i od ,i oq) The traditional solution to the unstable state is to increase the system damping or reduce the VSG output power. Increasing the system damping means increasing the virtual damping coefficient D of the VSG or increasing the virtual resistance in the virtual impedance. The present invention chooses to reduce the VSG output power, that is, appropriately reduce the power angle in the adjustment formula of δ(t), so that the output active power and reactive power are reduced, thereby reducing the energy of the system. The present invention chooses to use a mechanical switch to improve formula (10), that is, the power angle;

[0096] 3) When the energy function V(E d ,E q ,i od ,i oq ) is in a stable state, the mechanical switch is at position 0, and when the energy function V(E d ,E q ,i od ,i oq ) is in an unstable state, the mechanical switch is in the power angle compensation position, that is, the actual output power angle δ of VSG is:

[0097]

[0098] In formula (13), k w and are the integral compensation coefficients of the frequency deviation.

[0099] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the protection scope of the present invention.

[0100] Any matters not described in the present invention are applicable to the prior art.

Claims

1. An improved virtual synchronous machine control strategy based on function control, characterized in that The following steps are involved: Step 1: Establish a traditional virtual synchronous generator VSG control model; Step 2: Design the power angle adaptive control function; Step 3: Design a nonlinear power control function based on the energy function to perform power angle compensation.

2. The improved virtual synchronous machine control strategy based on function control according to claim 1 is characterized in that: In step 1, a traditional virtual synchronous generator control model is established, and the specific method is as follows: 1) The rotor mechanical equation of primary frequency modulation corresponding to the active power-frequency and reactive power-voltage control links of the virtual synchronous machine VSG is: (1)； In formula (1), J is the virtual moment of inertia, D is the virtual damping coefficient, Kp is the active frequency droop coefficient, Pm is the virtual mechanical power, PN is the rated input active power, Pe is the actual output power, w is the actual output angular frequency, w0 is the rated input angular frequency, is the actual output power angle of VSG, and t is the time; 2) The reactive power-voltage droop control equation of the virtual synchronous machine is: (2)； In formula (2), K q is the reactive voltage integral coefficient, K u is the reactive voltage droop coefficient, Q N is the rated input reactive power, Q e is the actual output reactive power, U N is the rated input phase voltage, U is the actual output phase voltage, and E is the VSG output electromotive force amplitude; 3) The dynamic characteristic curve of VSG transmitting power to the common coupling point can be expressed by the following formula: (3)； In formula (3), U s is the effective value of the input voltage on the power supply side, is the VSG transmission line impedance, U pcc is the grid coupling point voltage; 4) The active power Pe and reactive power Qe output by VSG can be expressed in the two-phase rotating coordinate system, i.e., the dq coordinate system, as follows: (4)； In formula (4), E d is the d-axis electromotive force, E q is the q-axis electromotive force, i od is the d-axis current, i oq is the q-axis current; 5) According to the corresponding parameter relationship between formula (8) and formula (9), we can know that: (5)； (6)。 3. The improved virtual synchronous machine control strategy based on function control according to claim 1 is characterized in that: In step 2, a power angle adaptive control function is designed, and the specific method is as follows: 1) The power angle adaptive control function is: (7)； In formula (7), is the initial output power angle of VSG, It is a nonlinear function that can perform adaptive adjustment of the power angle based on the disturbance changes of frequency and voltage; 2) According to formula (7), the nonlinear regulation function introduced by the VSG power angle adaptive control function takes the angular frequency deviation and voltage deviation as variables, and the deviations are: (8)； In formula (8), w ref and E ref are the reference frequency and reference voltage respectively, w(t) and E(t) are the frequency and voltage currently output by VSG; 3) Define the function for: (9)； In formula (9), and are the proportional and integral gains of the frequency deviation, is the proportional gain of the voltage deviation; 4) Substituting formula (9) into formula (7), the formula for the dynamic change of power angle is: (10)。 4. The grid-connected converter control strategy for coping with symmetrical grid voltage drop according to claim 1 is characterized in that: In step 3, a nonlinear power control function based on an energy function is designed to perform power angle compensation. The specific method is as follows: 1) The nonlinear energy control function is: (11)； V(E d ,E q ,i od ,i oq ) is an energy function, which can be used to evaluate the energy distribution and dissipation characteristics of the system, thereby achieving more accurate power control; 2) The energy function introduced in formula (11) is based on the Lyapunov function, so V(E d ,E q ,i od ,i oq ) is non-negative, and the derivative of this function yields: (12)； According to Lyapunov's stability criterion, if , then the Lyapunov function V(E d ,E q ,i od ,i oq ) decreases with time, the system tends to be stable. On the contrary, if , then the function V(E d ,E q ,i od ,i oq ) increases with time, the system is unstable, or is in a boundary stability state, and the energy function V(E d ,E q ,i od ,i oq ) The traditional solution to the unstable state is to increase the system damping or reduce the VSG output power. Increasing the system damping means increasing the virtual damping coefficient D of the VSG or increasing the virtual resistance in the virtual impedance. The present invention chooses to reduce the VSG output power, that is, appropriately reduce the power angle in the adjustment formula of δ(t), so that the output active power and reactive power are reduced, thereby reducing the energy of the system. The present invention chooses to use a mechanical switch to improve formula (10), that is, the power angle; 3) When the energy function V(E d ,E q ,i od ,i oq ) is in a stable state, the mechanical switch is at position 0, and when the energy function V(E d ,E q ,i od ,i oq ) is in an unstable state, the mechanical switch is in the power angle compensation position, that is, the actual output power angle of the VSG for: (13)； In formula (13), and are the integral compensation coefficients of the frequency deviation.

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