Adaptive gain integral feed-forward compensation virtual synchronous machine control strategy

Abstract

The invention discloses a control method of a self-adaptive gain integral feed-forward compensation virtual synchronous generator (VSG), belongs to the technical field of distributed energy grid-connected converters, and particularly relates to a control method of a self-adaptive gain integral feed-forward compensation virtual synchronous generator for improving system frequency and voltage supporting capacity. The method comprises a VSG control link, a secondary integration link and an integration feedforward compensation link. The VSG control link comprises primary frequency modulation control of active power-frequency and primary voltage regulation control of reactive power-voltage; the quadratic integration link comprises quadratic integration of the angular frequency difference and quadratic integration of the voltage difference; integral compensation is angular frequency difference and voltage difference feed-forward compensation in which a self-adaptive gain coefficient is introduced; the control strategy can effectively improve the frequency and voltage supporting capacity of the grid-connected system when the voltage of the power grid is sag, meanwhile, the electric energy quality is improved, and a new thought is provided for the technical development of the grid-connected converter.

Description

Technical Field

[0001] The invention discloses a virtual synchronous machine control method with adaptive gain integral feedforward compensation, which belongs to the technical field of distributed energy grid-connected converters, and in particular relates to a virtual synchronous generator control method with adaptive gain integral feedforward compensation for improving the frequency and voltage support capability of a grid-connected coupling point. Background Art

[0002] The grid-connected technology based on virtual synchronous machine can realize active support for grid voltage and frequency, avoiding the defects of lack of damping and inertia support of converters controlled by traditional power electronics when connected to the grid. In order to cope with the degradation of power quality caused by temporary sag of grid voltage, existing converters usually choose external reactive power compensation devices, such as shunt capacitors, static VAR compensators (SVCs), static synchronous compensators (STATCOMs), synchronous phase condensers, thyristor-switched capacitors (TSCs), etc. Selecting appropriate reactive power compensation devices can significantly improve the operating efficiency and stability of the power system, but it increases the operating and maintenance costs, and will also bring more control problems and safety hazards.

[0003] The virtual synchronous machine can simulate the traditional synchronous generator to provide inertia and damping characteristics for the power grid. By controlling the grid-connected converter, it can have a certain frequency and voltage support capability. The traditional virtual synchronous machine realizes primary frequency and voltage regulation based on droop control, and the primary regulation is differential regulation. In order to achieve zero-difference regulation of frequency and voltage, the virtual synchronous machine simulates the traditional generator for secondary frequency and voltage regulation, but it will lead to problems such as increased overshoot, increased fluctuations, and deterioration of power quality. Summary of the invention

[0004] In order to overcome the problems existing in the related art, the present invention discloses and implements an adaptive gain integral feedforward compensation virtual synchronous machine control strategy.

[0005] The technical solution adopted by the present invention is:

[0006] An adaptive gain integral feedforward compensation virtual synchronous machine control strategy, characterized by comprising the following steps:

[0007] Step 1: Establish active power-frequency and reactive power-voltage control models of virtual synchronous generators;

[0008] Step 2: Design the secondary integral control link of VSG angular frequency difference and voltage difference;

[0009] Step 3: Design an adaptive gain-based integral feedforward compensation link to adjust the VSG frequency and voltage support effect.

[0010] In step 1, a control model of a virtual synchronous machine is established, and the specific method is as follows:

[0011] 1) The active power-frequency and reactive power-voltage control links of the virtual synchronous machine both adopt droop control, and the rotor mechanical equation of the primary frequency modulation is:

[0012]

[0013] 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, w0 is the rated input angular frequency, θ is the actual output power angle of VSG, and t is the time;

[0014] 2) The reactive power-voltage droop control equation of the virtual synchronous machine is:

[0015]

[0016] 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 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;

[0017] By establishing active power-frequency and reactive power-voltage control models, the virtual synchronous generator can provide the power system with dynamic response functions similar to those of a synchronous generator. It is of great significance in improving grid stability, increasing the proportion of renewable energy access, and enhancing the autonomy of microgrids.

[0018] In step 2, the secondary integration link of the VSG angular frequency difference and the voltage difference is designed, and the specific method is as follows:

[0019] In VSG control, the purpose of designing the secondary integral link is to make the control of the frequency (angular frequency difference Δw) and voltage (voltage difference ΔU) of the common coupling point (PCC) more accurate and stable by introducing a dynamic response link. This design method can enhance the anti-disturbance ability of the virtual synchronous generator to grid disturbances and improve its regulation response speed.

[0020] 1) Define the angular frequency difference Δw and voltage difference ΔU between the common coupling point of VSG and the grid as:

[0021]

[0022] In formula (3), w is the actual output angular frequency, w0 is the rated input angular frequency, U N is the rated input phase voltage, U is the actual output phase voltage;

[0023] 2) The design of the frequency control link involves converting the angular frequency difference (Δw) into a control signal through a quadratic integration method, which is used to adjust the active power output of the VSG. According to the basic principle of integral control, the change of the angular frequency difference can be integrated so that the active power adjustment can accurately compensate for the deviation of the grid coupling point frequency;

[0024] ΔP=K1·Δω+K2·∫(Δω)dt (4);

[0025] In formula (4), K1 is the influence coefficient of frequency deviation on active power, and K2 is the accumulation effect of frequency deviation, that is, the inertial response of VSG is compensated by the integral link to further improve the frequency stability;

[0026] 3) The design of the voltage control link involves converting the voltage difference (ΔU) into a control signal through a quadratic integration method, which is used to adjust the reactive power output of the VSG. The regulation of reactive power not only adjusts the grid voltage immediately, but also copes with the long-term impact of voltage fluctuations through the integration link;

[0027] ΔQ=K3·ΔU+K4·∫(ΔU)dt (5);

[0028] In formula (5), K3 is the influence coefficient of voltage deviation on reactive power, K4 is the accumulation effect of voltage deviation, and the voltage recovery speed and stability are improved through the integral link;

[0029] 4) The model after the second integration of VSG is:

[0030]

[0031] In the complete control strategy of VSG, active power-frequency control and reactive power-voltage control are usually coupled together. The secondary integral link realizes comprehensive regulation by simultaneously controlling the diagonal frequency difference and voltage difference. The output signal of the integrated controller will adjust the active and reactive power of VSG to achieve optimal control of grid frequency and voltage.

[0032] In step 3, an adjustment of the integral feedforward compensation link based on adaptive gain is designed, and the specific method is as follows:

[0033] 1) The traditional feedforward compensation link uses a fixed gain when processing frequency and voltage deviations. In actual power grid operation, the changes in frequency and voltage are not only related to the current deviation, but also closely related to factors such as the type, amplitude, and frequency of the disturbance. The use of fixed-gain feedforward control will result in an inaccurate response. In this solution, the design of dynamic adaptive gain is introduced, that is, the gain K w (t) and K u (t) will be adjusted in real time according to the actual disturbance characteristics of the power grid. The gain size is determined by monitoring the disturbance amplitude and change speed of the power grid, and the integral feedforward compensation amount is dynamically adjusted. The mathematical expression of dynamic gain adjustment is:

[0034]

[0035] In formula (7), K w0 With K u0 are the initial gain coefficients of the angular frequency difference and the voltage difference, respectively. and It is a gain adjustment function based on the amplitude and rate of change of angular frequency and voltage, specifically:

[0036]

[0037] In formula (8), α1 and α2 are the angular frequency difference weight coefficients, which respectively determine the contribution of amplitude and rate to gain regulation, and β1 and β2 are the voltage difference weight coefficients, which respectively determine the influence of amplitude and rate on gain regulation;

[0038] 2) Integral feedforward compensation quickly responds to disturbances through integral adjustment of disturbance signals (frequency deviation and voltage deviation), eliminates residual errors in steady state, enhances the dynamic and steady-state performance of the system, realizes active compensation for disturbance response, and improves frequency and voltage support effects. The compensation formula is as follows:

[0039]

[0040] In formula (9), P comp (t) is the change in active power after integral feedforward compensation, Q comp (t) is the change in active power after integral feedforward compensation;

[0041] 3) Adding the integral feedforward compensation based on adaptive gain, the VSG control model is:

[0042]

[0043] The present invention provides an adaptive gain integral feedforward compensation virtual synchronous machine control strategy, and the technical effects are as follows:

[0044] 1) A secondary frequency and voltage regulation control method of VSG is designed to target external disturbances, which can achieve zero-difference regulation of the frequency and voltage at the common coupling point;

[0045] 2) The design of dynamic adaptive gain is introduced to adjust in real time according to the actual disturbance characteristics of the power grid. The gain size is determined by monitoring the disturbance amplitude and change speed of the power grid, and the integral feedforward compensation amount is dynamically adjusted;

[0046] 3) Adding integral feedforward compensation control can enhance the VSG’s active support capability for grid voltage and frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] 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;

[0048] Figure 1 A circuit diagram of a grid-connected converter provided in an embodiment of the present invention;

[0049] Figure 2 An improved virtual synchronous machine control diagram provided by an embodiment of the present invention;

[0050] Figure 3 A diagram of VSG output active power and VSG output reactive power provided by an embodiment of the present invention;

[0051] Figure 4 A diagram showing instantaneous changes in voltage and current at a grid-connected common coupling point provided by an embodiment of the present invention;

[0052] Figure 5 A diagram showing the effective value changes of the voltage and current at the grid-connected common coupling point provided by an embodiment of the present invention;

[0053] Figure 6 A comparison chart of output frequency changes between the improved VSG provided in an embodiment of the present invention and other control strategies. DETAILED DESCRIPTION

[0054] The following is combined with Figures 1 to 6 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.

[0055] Figure 1 This is a circuit diagram of a grid-connected converter provided in an embodiment of the present invention, wherein the voltage and current waveforms at the grid-connected coupling point directly reflect the power quality studied in this case.

[0056] Figure 2 The improved virtual synchronous machine control diagram provided by the embodiment of the present invention is established in the following steps:

[0057] Step 1: Establish active power-frequency and reactive power-voltage control models of virtual synchronous generators;

[0058] Step 2: Design the secondary integral control link of VSG angular frequency difference and voltage difference;

[0059] Step 3: Design an adaptive gain-based integral feedforward compensation link to adjust the VSG frequency and voltage support effect.

[0060] In step 1, a control model of a virtual synchronous machine is established, and the specific method is as follows:

[0061] 1) The active power-frequency and reactive power-voltage control links of the virtual synchronous machine both adopt droop control, and the rotor mechanical equation of the primary frequency modulation is:

[0062]

[0063] 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, w0 is the rated input angular frequency, θ is the actual output power angle of VSG, and t is the time;

[0064] 2) The reactive power-voltage droop control equation of the virtual synchronous machine is:

[0065]

[0066] 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 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;

[0067] By establishing active power-frequency and reactive power-voltage control models, the virtual synchronous generator can provide the power system with dynamic response functions similar to those of a synchronous generator. It is of great significance in improving grid stability, increasing the proportion of renewable energy access, and enhancing the autonomy of microgrids.

[0068] In step 2, the secondary integration link of the VSG angular frequency difference and the voltage difference is designed, and the specific method is as follows:

[0069] In VSG control, the purpose of designing the secondary integral link is to make the control of the frequency (angular frequency difference Δw) and voltage (voltage difference ΔU) of the common coupling point (PCC) more accurate and stable by introducing a dynamic response link. This design method can enhance the anti-disturbance ability of the virtual synchronous generator to grid disturbances and improve its regulation response speed.

[0070] 1) Define the angular frequency difference Δw and voltage difference ΔU between the common coupling point of VSG and the grid as:

[0071]

[0072] In formula (3), w is the actual output angular frequency, w0 is the rated input angular frequency, U N is the rated input phase voltage, U is the actual output phase voltage;

[0073] 2) The design of the frequency control link involves converting the angular frequency difference Δw into a control signal through a quadratic integration method, which is used to adjust the active power output of the VSG. According to the basic principle of integral control, the change of the angular frequency difference can be integrated so that the active power adjustment can accurately compensate for the deviation of the grid coupling point frequency;

[0074] ΔP=K1·Δω+K2·∫(Δω)dt (4);

[0075] In formula (4), K1 is the influence coefficient of frequency deviation on active power, and K2 is the accumulation effect of frequency deviation, that is, the inertial response of VSG is compensated by the integral link to further improve the frequency stability;

[0076] 3) The design of the voltage control link involves converting the voltage difference ΔU into a control signal through a quadratic integration method, which is used to adjust the reactive power output of the VSG. The regulation of reactive power not only adjusts the grid voltage immediately, but also copes with the long-term impact of voltage fluctuations through the integration link;

[0077] ΔQ=K3·ΔU+K4·∫(ΔU)dt (5);

[0078] In formula (5), K3 is the influence coefficient of voltage deviation on reactive power, K4 is the accumulation effect of voltage deviation, and the voltage recovery speed and stability are improved through the integral link;

[0079] 4) The model after the second integration of VSG is:

[0080]

[0081] In the complete control strategy of VSG, active power-frequency control and reactive power-voltage control are usually coupled together. The secondary integral link realizes comprehensive regulation by simultaneously controlling the diagonal frequency difference and voltage difference. The output signal of the integrated controller will adjust the active and reactive power of VSG to achieve optimal control of grid frequency and voltage.

[0082] In step 3, the integral feedforward compensation link adjustment based on adaptive gain is designed, and the specific method is as follows:

[0083] 1) The traditional feedforward compensation link uses a fixed gain when processing frequency and voltage deviations. In actual power grid operation, the changes in frequency and voltage are not only related to the current deviation, but also closely related to factors such as the type, amplitude, and frequency of the disturbance. The use of fixed-gain feedforward control will result in an inaccurate response. In this solution, the design of dynamic adaptive gain is introduced, that is, the gain K w (t) and K u (t) will be adjusted in real time according to the actual disturbance characteristics of the power grid. The gain size is determined by monitoring the disturbance amplitude and change speed of the power grid, and the integral feedforward compensation amount is dynamically adjusted. The mathematical expression of dynamic gain adjustment is:

[0084]

[0085] In formula (7), K w0 With K u0 are the initial gain coefficients of the angular frequency difference and the voltage difference, respectively. and It is a gain adjustment function based on the amplitude and rate of change of angular frequency and voltage, specifically:

[0086]

[0087] In formula (8), α1 and α2 are the angular frequency difference weight coefficients, which respectively determine the contribution of amplitude and rate to gain regulation, and β1 and β2 are the voltage difference weight coefficients, which respectively determine the influence of amplitude and rate on gain regulation;

[0088] 2) Integral feedforward compensation quickly responds to disturbances through integral adjustment of disturbance signals (frequency deviation and voltage deviation), eliminates residual errors in steady state, enhances the dynamic and steady-state performance of the system, realizes active compensation for disturbance response, and improves frequency and voltage support effects. The compensation formula is as follows:

[0089]

[0090] In formula (9), P comp (t) is the change in active power after integral feedforward compensation, Q comp(t) is the change in active power after integral feedforward compensation;

[0091] 3) Adding the integral feedforward compensation based on adaptive gain, the VSG control model is:

[0092]

[0093] Example: During the stable operation of the grid-connected converter, the grid voltage is set to temporarily drop at t=0.8s, and the drop degree is 20% of the rated value. The grid voltage returns to the rated value at t=1.5s. In this example, the grid line voltage is 380V, the rated output active power of the VSG is 70kW, and the rated output reactive power is 40kVar.

[0094] Figure 3 The VSG output active power and VSG output reactive power diagram provided in the embodiment of the present invention show that the stable values ​​of active power and reactive power before and after the grid voltage drops are different from the rated values ​​due to line loss. When the voltage drops at t=0.8s, the VSG output active power and reactive power increase in order to provide active support for voltage and frequency. Figure 4 The instantaneous change diagram of the voltage and current at the grid-connected common coupling point provided in the embodiment of the present invention sets the voltage drop ratio to 20%, and the actual drop ratio is only 2%; Figure 5 The effective value change diagram of the voltage and current at the grid-connected common coupling point provided by the embodiment of the present invention shows that when the actual voltage drop ratio at the coupling point is only 2%, the effective value change of the voltage only shows a slight fluctuation, which fully verifies that the voltage support capability of the present method is very good, and the current can change rapidly to stability; Figure 6 The comparison chart of the output frequency changes of the improved VSG provided in the embodiment of the present invention and other control strategies fully verifies that the frequency support effect of the present control method is superior to that of the prior art.

[0095] 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 within the protection scope of the present invention.

[0096] Any matters not described in the present invention are applicable to the prior art.

Claims

1. An adaptive gain integral feedforward compensation virtual synchronous machine control strategy, characterized in that The following steps are involved: Step 1: Establish active power-frequency and reactive power-voltage control models of virtual synchronous generators; Step 2: Design the secondary integral control link of VSG angular frequency difference and voltage difference; Step 3: Design an adaptive gain-based integral feedforward compensation link to adjust the VSG frequency and voltage support effect.

2. The control strategy of virtual synchronous machine based on adaptive gain integral feedforward compensation according to claim 1 is characterized in that: In step 1, an active power-frequency and reactive power-voltage control model of a virtual synchronous generator is established, and the specific method is as follows: 1) The active power-frequency and reactive power-voltage control links of the virtual synchronous machine both adopt droop control, and the rotor mechanical equation of the primary frequency modulation is: 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, w0 is the rated input angular frequency, θ 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: 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 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; By establishing active power-frequency and reactive power-voltage control models, the virtual synchronous generator can provide the power system with dynamic response functions similar to those of a synchronous generator. It is of great significance in improving grid stability, increasing the proportion of renewable energy access, and enhancing the autonomy of microgrids.

3. The control strategy of virtual synchronous machine based on adaptive gain integral feedforward compensation according to claim 1 is characterized in that: In step 2, the secondary integration link of the VSG angular frequency difference and the voltage difference is designed, and the specific method is as follows: In VSG control, the purpose of designing the secondary integral link is to make the control of the frequency (angular frequency difference Δw) and voltage (voltage difference ΔU) of the common coupling point (PCC) more accurate and stable by introducing a dynamic response link. This design method can enhance the anti-disturbance ability of the virtual synchronous generator to grid disturbances and improve its regulation response speed. 1) Define the angular frequency difference Δω and voltage difference ΔU between the common coupling point of VSG and the grid as: In formula (3), w is the actual output angular frequency, w0 is the rated input angular frequency, U N is the rated input phase voltage, U is the actual output phase voltage; 2) The design of the frequency control link involves converting the angular frequency difference Δw into a control signal through a quadratic integration method, which is used to adjust the active power output of the VSG. According to the basic principle of integral control, the change of the angular frequency difference can be integrated so that the active power adjustment can accurately compensate for the deviation of the PCC frequency at the grid coupling point; ΔP=K1·Δω+K2·∫(Δω)dt (4); In formula (4), K1 is the influence coefficient of frequency deviation on active power, and K2 is the accumulation effect of frequency deviation, that is, the inertial response of VSG is compensated by the integral link to further improve the frequency stability; 3) The design of the voltage control link involves converting the voltage difference ΔU into a control signal through a quadratic integration method, which is used to adjust the reactive power output of the VSG. The regulation of reactive power not only adjusts the grid voltage immediately, but also copes with the long-term impact of voltage fluctuations through the integration link; ΔQ=K3·ΔU+K4·∫(ΔU)dt (5); In formula (5), K3 is the influence coefficient of voltage deviation on reactive power, K4 is the accumulation effect of voltage deviation, and the voltage recovery speed and stability are improved through the integral link; 4) The model after the second integration of VSG is: In the complete control strategy of VSG, active power-frequency control and reactive power-voltage control are usually coupled together. The secondary integral link realizes comprehensive regulation by simultaneously controlling the diagonal frequency difference and voltage difference. The output signal of the integrated controller will adjust the active and reactive power of VSG to achieve optimal control of grid frequency and voltage.

4. The control strategy of virtual synchronous machine based on adaptive gain integral feedforward compensation according to claim 1 is characterized in that: In step 3, the integral feedforward compensation link adjustment based on adaptive gain is designed, and the specific method is as follows: 1) The traditional feedforward compensation link uses a fixed gain when processing frequency and voltage deviations. In actual power grid operation, the changes in frequency and voltage are not only related to the current deviation, but also closely related to factors such as the type, amplitude, and frequency of the disturbance. The use of fixed-gain feedforward control will result in an inaccurate response. In this solution, the design of dynamic adaptive gain is introduced, that is, the gain K w (t) and K u (t) will be adjusted in real time according to the actual disturbance characteristics of the power grid. The gain size is determined by monitoring the disturbance amplitude and change speed of the power grid, and the integral feedforward compensation amount is dynamically adjusted. The mathematical expression of dynamic gain adjustment is: In formula (7), K w0 With K u0 are the initial gain coefficients of the angular frequency difference and the voltage difference, respectively. and It is a gain adjustment function based on the amplitude and rate of change of angular frequency and voltage, specifically: In formula (8), α1 and α2 are the angular frequency difference weight coefficients, which respectively determine the contribution of amplitude and rate to gain regulation, and β1 and β2 are the voltage difference weight coefficients, which respectively determine the influence of amplitude and rate on gain regulation; 2) Integral feedforward compensation quickly responds to disturbances through integral adjustment of disturbance signals (frequency deviation and voltage deviation), eliminates residual errors in steady state, enhances the dynamic and steady-state performance of the system, realizes active compensation for disturbance response, and improves frequency and voltage support effects. The compensation formula is as follows: In formula (9), P comp (t) is the change in active power after integral feedforward compensation, Q comp (t) is the change in active power after integral feedforward compensation; 3) Adding the integral feedforward compensation based on adaptive gain, the VSG control model is:

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