Static var generator grid-connected renewable energy power station coordination control system and method with active power supporting capability

Abstract

The invention discloses a static var generator grid-connected renewable energy power station coordination control system and method with an active power supporting capability, and relates to the technical field of power system control. The static var generator is used for providing reactive power support and dynamically adjusting active power based on four-quadrant operation characteristics when the power grid frequency fluctuates; and the combined frequency and voltage regulation and control unit is used for regulating and controlling the frequency and the voltage of the power grid and coordinating and controlling the operation states of the virtual synchronous generator and the static var generator based on a regulation and control result. According to the invention, cooperative control is carried out on the static var generator with the four-quadrant operation capability and the virtual synchronous generator with the network construction capability, and combined dynamic adjustment of active power and reactive power is realized under a unified control framework; the stable supporting capacity of the new energy power station under the power grid disturbance conditions of voltage sag, frequency fluctuation and the like is remarkably enhanced, and the autonomous response and adjustment capacity of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system control. Specifically, it relates to a coordinated control system and method for a grid-connected renewable energy power station with a static var generator having active power support capabilities. Background Art

[0002] With the continuous increase in the penetration rate of renewable energy power generation in the power system, the inertia level and damping characteristics of the power system have decreased significantly, leading to severe challenges in frequency stability and voltage stability. Traditional synchronous generators provide frequency support for the power grid through mechanical rotational inertia, while renewable energy power generation units (such as wind turbines and photovoltaic inverters) are usually connected to the grid through power electronic converters. Their inherent low inertia and weak damping characteristics are prone to causing frequency fluctuations and voltage instability problems. To address the above challenges, it is urgent to develop safe, reliable, and efficient coordinated control technologies to adapt to renewable energy fluctuations and grid disturbances and ensure the stable operation of a high-penetration renewable energy power system.

[0003] In the field of grid-forming control technology, virtual synchronous generators (VSGs) have received extensive attention because they can simulate the external characteristics of synchronous generators. Through the adjustment of virtual inertia and damping coefficients, VSGs can enhance the grid support ability of converters, especially having significant advantages in weak grid scenarios. However, the active power output of VSGs is limited by the fluctuations in renewable energy output and it is difficult to independently achieve rapid power rebalancing in the event of a grid fault and relies on external devices to provide auxiliary support.

[0004] Currently, the power system often configures energy storage devices (ESSs) and reactive power compensation devices to make up for the power regulation defects of renewable energy power generation units. Although energy storage systems can provide short-term power support through charging and discharging, their economy is limited by the high-capacity configuration requirements of 10%-20% of the grid-connected capacity; as a dynamic reactive power compensation device, a static var generator (SVG) can suppress voltage fluctuations and improve the power factor, but traditional static var generators only have reactive power regulation functions and lack active power support capabilities and cannot directly participate in system frequency regulation.

[0005] Existing coordinated control technologies mostly focus on the optimization of traditional reactive power compensation devices or single control objects. For example, the coordinated control of wind turbines and static var generators is used to suppress sub-synchronous oscillations; the STATCOM controller is adopted in the photovoltaic system to enhance voltage stability; the combined application of SVG and D-STATCOM realizes the dynamic reactive power compensation of the AC-DC interconnected system. However, these methods have not established a coordinated control mechanism for grid-forming converters and static var generators with active power support capabilities, and it is difficult to meet the requirements of the new power system for rapid response and joint regulation in multi-disturbance scenarios. Especially in the scenarios of grid faults (such as voltage sags and short-circuit faults), the response speed and regulation accuracy of existing strategies are still insufficient. For example, traditional PI control relies on the initial state to achieve voltage recovery and cannot guarantee the convergence performance within the preset time; the existing static var generator control technology does not integrate the active power support function, resulting in a decline in system frequency stability when the active power output of the VSG is limited; there is a lack of dynamic stability region analysis and parameter coordinated tuning methods for the combined system of grid-forming converters and static var generators. In the existing technology, although the parallel control strategy of VSG and static var generator proposed in "Power System Technology" optimizes the transient stability through the power angle characteristic, the static var generator only provides reactive power output and does not involve frequency support; although the research in "Power System Protection and Control" focuses on the transient recovery voltage, it does not limit the voltage recovery time; although the energy storage type static var generator proposed in "High Voltage Engineering" has the inertia response ability, it does not involve the multi-device coordinated control strategy.

[0006] In summary, there is still a lack of a complete set of control methods for the coordinated operation of static var generators with active power support capabilities and grid-forming converters in the existing technology system. Especially in terms of achieving rapid response, precise regulation, and comprehensive improvement of system stability in multi-disturbance scenarios, there are still obvious technical gaps.

[0007] In response to the problems in the related technologies, no effective solutions have been proposed yet. Summary of the Invention

[0008] In response to the problems in the related technologies, the present invention proposes a coordinated control system and method for a grid-connected renewable energy power station with a static var generator having active power support capabilities to overcome the above technical problems existing in the existing related technologies.

[0009] Therefore, the specific technical solutions adopted by the present invention are as follows:

[0010] According to one aspect of the present invention, there is provided a coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capabilities, the system comprising:

[0011] A virtual synchronous generator, which is used to simulate the external electrical characteristics of a synchronous generator and inject the active power generated by a renewable energy power generation device into the power grid;

[0012] A static var generator, which is used to provide reactive power support and dynamically adjust the active power based on the four - quadrant operation characteristics when the power grid frequency fluctuates;

[0013] A combined frequency - voltage regulation unit, which is used to regulate the power grid frequency and voltage and coordinately control the operating states of the virtual synchronous generator and the static var generator based on the regulation results.

[0014] Optionally, the static var generator includes:

[0015] A mathematical model construction module, which is used to collect electrical parameters based on the four - quadrant operation characteristics and construct a mathematical model of the dynamic coupling of active power and reactive power between the static var generator and the power grid based on the electrical parameters;

[0016] A dynamic constraint condition setting module, which is used to calculate the maximum active power output by the static var generator according to the maximum current limit of the static var generator, combined with the output voltage of the energy storage converter and the power grid current, and set the maximum active power as the corresponding dynamic constraint condition;

[0017] A state detection module, which is used to detect the fluctuations of the power grid voltage and the power grid frequency.

[0018] Optionally, the expression of the mathematical model is:

[0019]

[0020] In the formula, P represents the active power of the static var generator; V svg represents the output voltage of the static var generator; V pcc represents the power grid voltage; δ represents the angle between the output voltage of the static var generator and the power grid voltage; Q represents the reactive power of the static var generator; ω represents the angular velocity of the power grid; L represents the value of the filter inductor;

[0021] The expression of the dynamic constraint condition is:

[0022]

[0023] In the formula, P max represents the maximum active power output by the static var generator; Q represents the reactive power of the static var generator; V ap represents the output voltage of the energy storage part of the static var generator; V pcc represents the power grid voltage.

[0024] Optionally, the combined frequency - voltage regulation unit includes:

[0025] A voltage droop control module, which is used to trigger a preset voltage-reactive power droop mechanism according to the grid voltage detection result, adjust the output of reactive power to achieve primary voltage regulation, and combine a voltage controller based on fixed-time stability to perform secondary voltage regulation;

[0026] A frequency droop control module, which is used to trigger a preset frequency-active power droop mechanism based on the grid frequency detection result, and combine the four-quadrant operation characteristics of a static var generator to construct a virtual power channel and perform frequency regulation.

[0027] Optionally, the expression of the voltage-reactive power droop mechanism is:

[0028] V ref -V pcc =K dQ (Q′ ref -Q0);

[0029] In the formula, V ref represents the voltage reference value; V pcc represents the grid voltage; K dQ represents the reactive power control droop coefficient; Q′ ref represents the reactive power reference value generated by droop control; Q0 represents the reactive power base value of the static var generator;

[0030] The expression of the frequency-active power droop mechanism is:

[0031] f ref -f=K dP (P - P0);

[0032] In the formula, f ref represents the frequency reference value; f represents the frequency; K dP represents the active power control droop coefficient; P represents the active power of the static var generator; P0 represents the active power base value of the static var generator.

[0033] Optionally, the voltage droop control module includes:

[0034] A primary voltage regulation sub-module, which is used to trigger a preset voltage-reactive power droop mechanism according to the voltage deviation degree by the static var generator when the grid voltage drop is detected, calculate the initial reactive power reference value, and inject the corresponding reactive power to achieve primary voltage regulation;

[0035] A secondary voltage regulation sub-module, which is used to design a voltage controller based on the fixed-time stability theory according to the result of the primary voltage regulation and perform secondary voltage regulation to correct the voltage deviation.

[0036] Optionally, the expression of the voltage controller is:

[0037]

[0038] wherein, u represents the input of secondary voltage control; c1 represents a control parameter; V pcc represents the grid voltage; V nom represents the nominal voltage of the coordinated control system; κ1 represents a positive odd number; κ2 represents a positive odd number; c2 represents a control parameter.

[0039] Optionally, the frequency droop control module includes:

[0040] An active power adjustment sub-module, configured to, when detecting a decrease in the grid frequency, trigger a preset frequency-active power droop mechanism according to the degree of frequency deviation by the static var generator, and calculate a reference value of the active power in combination with a fast frequency response framework, so as to adjust the output of the active power;

[0041] A virtual power channel construction sub-module, configured to construct a virtual power channel between the static var generator and the virtual synchronous generator in combination with the active power adjustment result and the four-quadrant operation characteristics of the static var generator;

[0042] A frequency regulation sub-module, configured to, based on the constructed virtual power channel, when the static var generator outputs reactive power to support the voltage, dynamically absorb the active power output by the virtual synchronous generator, so as to realize the frequency regulation between the virtual synchronous generator and the static var generator.

[0043] Optionally, when the static var generator outputs reactive power to support the voltage, the expression for dynamically absorbing the active power output by the virtual synchronous generator is:

[0044]

[0045] wherein, P APSC-SVG represents the active power of the static var generator; P max represents the maximum active power output by the static var generator; P VSG represents the active power of the virtual synchronous generator.

[0046] According to another aspect of the present invention, there is also provided a coordinated control method for a static var generator grid-connected renewable energy power station with active power support ability, and the method includes:

[0047] S1. Simulate the external electrical characteristics of a synchronous generator, inject the active power generated by the renewable energy power generation equipment into the grid, and detect the fluctuation changes of the grid voltage and frequency according to the response situation during the injection process;

[0048] S2. According to the grid voltage detection result, trigger the preset voltage-reactive power droop mechanism, adjust the output of reactive power to achieve primary voltage regulation, and combine with the voltage controller based on fixed-time stability to perform secondary voltage regulation;

[0049] S3. Based on the grid frequency detection result, trigger the preset frequency-active power droop mechanism, and combine with the four-quadrant operation characteristics of the static var generator to construct a virtual power channel and perform frequency regulation;

[0050] S4. Combine the results of voltage regulation and frequency regulation, and coordinate the active power interaction between the virtual synchronous generator and the static var generator to achieve coordinated operation.

[0051] The beneficial effects of the present invention are as follows:

[0052] 1. By coordinately controlling the static var generator with four-quadrant operation ability and the virtual synchronous generator with grid-forming ability, the present invention realizes the joint dynamic regulation of active and reactive power under a unified control framework, significantly enhances the stable support ability of the new energy power station under grid disturbances such as voltage sags and frequency fluctuations, gets rid of the dependence on external energy storage systems, and improves the autonomous response and regulation ability of the system.

[0053] 2. By introducing the fixed-time stability theory into the voltage recovery control, the present invention realizes the voltage recovery within a predetermined time regardless of the initial disturbance conditions, significantly improves the control accuracy and fault response speed, and enhances the adaptability and robustness of the system.

[0054] 3. By constructing a virtual power channel and introducing a dynamic power distribution mechanism, the present invention realizes the coordinated control of active power between the VSG and the SVG, enables the SVG to actively absorb the redundant power of the VSG during faults, effectively alleviates the problems of energy accumulation and overvoltage on the DC side, and improves the engineering applicability and promotion value of the system. Description of the Drawings

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0056] Figure 1 It is a principle block diagram of a coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support ability according to an embodiment of the present invention;

[0057] Figure 2It is a flowchart of a coordinated control method for a grid-connected renewable energy power station with a static var generator having active power support capability according to an embodiment of the present invention;

[0058] Figure 3 It is a structural diagram of a system in which a VSG and an APSC-SVG are connected in parallel to the grid in a coordinated control method for a grid-connected renewable energy power station with a static var generator having active power support capability according to an embodiment of the present invention;

[0059] Figure 4 It is a vector diagram of an APSC-SVG connected to the grid in a coordinated control method for a grid-connected renewable energy power station with a static var generator having active power support capability according to an embodiment of the present invention;

[0060] Figure 5 It is a power characteristic diagram of an APSC-SVG in a coordinated control method for a grid-connected renewable energy power station with a static var generator having active power support capability according to an embodiment of the present invention;

[0061] Figure 6 It is the overall control framework of an APSC-SVG in a coordinated control method for a grid-connected renewable energy power station with a static var generator having active power support capability according to an embodiment of the present invention.

[0062] In the figure:

[0063] 1. Virtual synchronous generator; 2. Static var generator; 3. Combined frequency and voltage regulation unit. Specific embodiments

[0064] To further illustrate each embodiment, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. They are mainly used to illustrate the embodiments and can be used to explain the operating principle of the embodiments in conjunction with the relevant descriptions in the specification. With reference to these contents, those of ordinary skill in the art should be able to understand other possible implementation manners and the advantages of the present invention.

[0065] According to an embodiment of the present invention, there is provided a coordinated control system and method for a grid-connected renewable energy power station with a static var generator having active power support capability.

[0066] Now, the present invention will be further described in conjunction with the accompanying drawings and specific embodiments. As Figure 1 shown, a coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capability according to an embodiment of the present invention includes:

[0067] A virtual synchronous generator 1, which is used to simulate the external electrical characteristics of a synchronous generator and inject the active power generated by the renewable energy power generation equipment into the grid.

[0068] It should be noted that the virtual synchronous generator (VSG) adopts a grid-forming control strategy. The grid-forming converter controlled by it can generate the voltage amplitude and phase angle through the power loop, and has strong grid support ability in weak grid scenarios. In the overall control framework, its outer control loop adopts the VSG control scheme, and the dynamic characteristics of its grid-connected inverter are as follows:

[0069]

[0070] In the formula, T m represents the equivalent mechanical input torque; T e represents the electromagnetic output torque; P eref represents the active power reference value; P Δf represents the additional active power adjustment amount under frequency disturbance; P e represents the actual output active power; ω0 represents the grid reference angular frequency; ω v represents the current angular frequency of the virtual synchronous motor; J represents the moment of inertia constant; K D represents the virtual damping coefficient; t represents time.

[0071] θ v = ∫ω v dt;

[0072] In the formula, θ v represents the phase angle of the output voltage; ω v represents the current angular frequency of the virtual synchronous motor; t represents time.

[0073] V v = U ref + K Q ∫(Q eref - Q e )dt;

[0074] In the formula, V v represents the output voltage amplitude; U ref represents the voltage reference value; Q eref represents the target reactive power; Q e represents the actual output reactive power; K Q represents the voltage-reactive power regulation coefficient; t represents time.

[0075] The static var generator 2 is used to provide reactive power support and dynamically adjust the active power based on the four-quadrant operation characteristics when the grid frequency fluctuates.

[0076] It should be noted that the static var generator is a static var generator with active power support ability (APSC-SVG); such as Figure 3As shown in the figure, the structural diagram of the system in which VSG and APSC-SVG are connected in parallel to the power grid. Renewable energy power generation stations are usually equipped with reactive power compensation devices at the point of common coupling (PCC) to ensure voltage stability.

[0077] APSC-SVG can not only stabilize the voltage at the PCC, but also provide frequency support in the case of power fluctuations of VSG, as Figure 4 shown, is the vector diagram of APSC-SVG connected to the power grid.

[0078] Preferably, the static var generator 2 includes:

[0079] A mathematical model construction module, which is used to collect electrical parameters based on the four-quadrant operation characteristics, and construct a mathematical model of the dynamic coupling of active power and reactive power between the static var generator and the power grid based on the electrical parameters.

[0080] Preferably, the expression of the mathematical model is:

[0081]

[0082] In the formula, P represents the active power of the static var generator; V svg represents the output voltage of the static var generator; V pcc represents the grid voltage; δ represents the angle between the output voltage of the static var generator and the grid voltage; Q represents the reactive power of the static var generator; ω represents the grid angular velocity; L represents the value of the filter inductor.

[0083] A dynamic constraint condition setting module, which is used to calculate the maximum active power output by the static var generator according to the maximum current limit of the static var generator, combined with the output voltage of the energy storage converter and the grid current, and set the maximum active power as the corresponding dynamic constraint condition.

[0084] The expression of the dynamic constraint condition is:

[0085]

[0086] In the formula, P max represents the maximum active power output by the static var generator; Q represents the reactive power of the static var generator; V ap represents the output voltage of the energy storage part of the static var generator; V pcc represents the grid voltage.

[0087] A state detection module, which is used to detect the fluctuations of the grid voltage and the grid frequency.

[0088] The active power and reactive power injected by APSC-SVG into the power grid are respectively:

[0089]

[0090] In the formula, P represents the active power of the static var generator; V svg represents the output voltage of the static var generator; V pcc represents the grid voltage; δ represents the angle between the output voltage of the static var generator and the grid voltage; Q represents the reactive power of the static var generator; ω represents the grid angular velocity; L represents the value of the filter inductor.

[0091] Due to the limitation of the maximum current I max of the device, the output of the active and reactive powers is restricted, that is:

[0092] P 2 +Q 2 =(3V pcc I) 2 ≤(3V pcc I max ) 2 ;

[0093] In the formula, P represents the active power of the static var generator; Q represents the reactive power of the static var generator; V pcc represents the grid voltage; I represents the output current of the static var generator; I max represents the maximum output current of the static var generator.

[0094] Although the energy storage part can provide active power and reactive power, in order to maximize the active power, the output voltage of the energy storage converter must be consistent with or opposite to the grid current. Therefore, the following relationship holds:

[0095]

[0096] In the formula, V pcc represents the grid voltage; represents the power factor of the coordinated control system; V ap represents the output voltage of the energy storage part; V rp represents the effective value of the output voltage of the capacitive part; ω represents the grid angular velocity; L represents the value of the filter inductor; I represents the output current of the static var generator; P max represents the maximum active power output by the static var generator; Q represents the reactive power of the static var generator.

[0097] Thus, it can be obtained that:

[0098]

[0099] In the formula, P max represents the maximum active power output by the static var generator; Q represents the reactive power of the static var generator; V apRepresents the output voltage of the energy storage part of the static var generator; V pcc Represents the grid voltage.

[0100] Considering the maximum output voltage constraint of the energy storage module, V ap There is a maximum value. Considering that the cascaded circuit often adopts carrier phase-shifted sinusoidal pulse width modulation (CPS-SPWM), the following is obtained:

[0101]

[0102] In the formula, V ap_max Represents the maximum output voltage of the energy storage part of the static var generator; V dc_bess Represents the DC voltage of the battery energy storage system.

[0103] The maximum active power that APSC-SVG can provide is:

[0104]

[0105] In the formula, P max Represents the maximum active power output by the static var generator; Q represents the reactive power of the static var generator; V grid Represents the grid voltage; V dc_bess Represents the DC voltage of the battery energy storage system.

[0106] Therefore, when the reactive power of the system is determined, the output range of the active power can be obtained according to the DC voltage on the energy storage side and the grid voltage; as Figure 5 shown, it is the power characteristic diagram of APSC-SVG, where the shaded area is the working range of APSC-SVG. Within this range, APSC-SVG can flexibly adjust the output of the active power.

[0107] The combined frequency and voltage regulation unit 3 is used to regulate the grid frequency and voltage, and coordinate and control the operating states of the virtual synchronous generator and the static var generator based on the regulation results.

[0108] Preferably, the combined frequency and voltage regulation unit 3 includes:

[0109] The voltage droop control module is used to trigger a preset voltage-reactive power droop mechanism according to the grid voltage detection result, adjust the output of the reactive power to achieve primary voltage regulation, and perform secondary voltage regulation in combination with a voltage controller based on fixed-time stability.

[0110] Preferably, the expression of the voltage-reactive power droop mechanism is:

[0111] V ref -V pcc =K dQ (Q ref-Q0);

[0112] Wherein, V ref represents the voltage reference value; V pcc represents the grid voltage; K dQ represents the droop coefficient of reactive power control; Q' ref represents the reactive power reference value generated by droop control; Q0 represents the reactive power base value of the static var generator.

[0113] Preferably, the voltage droop control module includes:

[0114] The primary voltage regulation sub-module is used to trigger a preset voltage-reactive power droop mechanism according to the degree of voltage deviation when the grid voltage drop is detected, calculate the initial reactive power reference value, and inject the corresponding reactive power to achieve primary voltage regulation;

[0115] The secondary voltage regulation sub-module is used to design a voltage controller based on the results of the primary voltage regulation by using the fixed-time stability theory and perform secondary voltage regulation to correct the voltage deviation.

[0116] Preferably, the expression of the voltage controller is:

[0117]

[0118] Wherein, u represents the input of secondary voltage control; c1 represents the control parameter; V pcc represents the grid voltage; V nom represents the nominal voltage of the coordinated control system; κ1 represents a positive odd number; κ2 represents a positive odd number; c2 represents the control parameter.

[0119] The frequency droop control module is used to trigger a preset frequency-active power droop mechanism based on the grid frequency detection result, and construct a virtual power channel in combination with the four-quadrant operation characteristics of the static var generator to perform frequency regulation.

[0120] The expression of the frequency-active power droop mechanism is:

[0121] f ref -f = K dP (P - P0);

[0122] Wherein, f ref represents the frequency reference value; f represents the frequency; K dP represents the droop coefficient of active power control; P represents the active power of the static var generator; P0 represents the active power base value of the static var generator.

[0123] Preferably, the frequency droop control module includes:

[0124] The active power adjustment sub-module is used to trigger a preset frequency-active power droop mechanism according to the degree of frequency deviation when the grid frequency drops, and calculate the active power reference value in combination with the fast frequency response framework to adjust the output of the active power;

[0125] The virtual power channel construction sub-module is used to construct a virtual power channel between the static var generator and the virtual synchronous generator by combining the active power adjustment result and the four-quadrant operation characteristics of the static var generator;

[0126] The frequency regulation sub-module is used to dynamically absorb the active power output by the virtual synchronous generator while the static var generator outputs reactive power to support the voltage based on the constructed virtual power channel, so as to realize the frequency regulation between the virtual synchronous generator and the static var generator.

[0127] Preferably, when the static var generator outputs reactive power to support the voltage, the expression for dynamically absorbing the active power output by the virtual synchronous generator is:

[0128]

[0129] In the formula, P APSC-SVG represents the active power of the static var generator; P max represents the maximum active power output by the static var generator; P VSG represents the active power of the virtual synchronous generator.

[0130] It should be added that for the photovoltaic generator set connected to the grid in the VSG control mode, by integrating APSC-SVG at the PV power supply node, the effectiveness of voltage recovery is improved, the low-voltage ride-through ability is realized, and the economic efficiency and operation safety of the system are balanced.

[0131] When the grid voltage sag is detected, the system preferentially establishes an initial reactive power support reference value through the voltage-reactive power droop control mechanism, and the droop characteristic can be expressed as:

[0132] V ref -V pcc =K dQ (Q ref -Q0);

[0133] In the formula, V ref represents the voltage reference value; V pcc represents the grid voltage; K dQ represents the reactive power control droop coefficient; Q′ ref represents the reactive power reference value generated by the droop control; Q0 represents the reactive power base value of the static var generator.

[0134] The inherent drawback of droop control lies in its static voltage deviation (SVD). To eliminate the SVD, secondary voltage regulation control must be introduced. Finally, the reactive power reference value is given by the following formula:

[0135] Q ref =Q ref +u;

[0136] In the formula, Q ref represents the final reactive power reference value; Q′ ref represents the reactive power reference value generated by droop control; u represents the input of secondary voltage control, which is obtained through timed secondary voltage control.

[0137] Utilizing the four - quadrant operation ability of APSC - SVG, the system dynamically adjusts the active power absorption to stabilize the frequency; a virtual power channel is constructed through the four - quadrant operation of APSC - SVG, that is, a two - way path for active power exchange between VSG and APSC - SVG; while outputting reactive power to support the voltage, APSC - SVG actively absorbs the active power generated by VSG and dynamically calculates the absorption upper limit. Therefore, during a voltage sag, the active powers of APSC - SVG and VSG are given by the following formula:

[0138]

[0139] In the formula, P APSC-SVG represents the active power of the static var generator; P max represents the maximum active power output by the static var generator; P VSG represents the active power of the virtual synchronous generator.

[0140] Therefore, the above - proposed strategy can effectively achieve the joint optimization of reactive power support and active power absorption during faults through the coordination of VSG and the four - quadrant operation of APSC - SVG.

[0141] Due to the random fluctuations of solar irradiance and the lack of rotational inertia in photovoltaic power generation, the active power output has great uncertainty, which may cause system frequency instability. To solve this problem, the system integrates the active power control ability of APSC - SVG into the frequency regulation mechanism; this integration introduces the P - f droop control strategy and combines it with the ESS - assisted fast frequency response (FFR) framework. Specifically, when the system frequency is detected to decrease, the SVG dynamically adjusts the active power absorption command according to the predefined droop characteristics. The formula for generating this reference value is as follows:

[0142] f ref -f = K dP (P - P0);

[0143] In the formula, f refdenotes the frequency reference value; f denotes the frequency; K dP denotes the active power control droop coefficient; P denotes the active power of the static var generator; P0 denotes the active power base value of the static var generator.

[0144] When the system voltage drops, the active power absorption value of the APSC-SVG is given by the active powers of the APSC-SVG and the VSG to minimize the curtailment of wind and solar power as much as possible. The overall control block diagram is as Figure 6 shown.

[0145] In addition, in order to be applied to new energy power stations with large fluctuations in new energy output power and a relatively fragile power grid, a voltage controller is designed using the fixed-time stability theory, which can achieve the rapid recovery of the power grid voltage.

[0146] Taking the derivative of both sides of the droop characteristic expression, we can obtain:

[0147]

[0148] In the formula, denotes the derivative of the power grid voltage; K dQ denotes the reactive power control droop coefficient; denotes the derivative of the reactive power reference value generated by the droop control.

[0149] Therefore:

[0150]

[0151] In the formula, denotes the derivative of the reactive power reference value generated by the droop control; K dQ denotes the reactive power control droop coefficient; denotes the derivative of the power grid voltage; u denotes the input of the secondary voltage control.

[0152] The reactive power support response time directly affects the speed of PCC voltage regulation. To achieve fast and precise voltage regulation of the integrated energy storage SVG at the PCC and enhance the controllability of the voltage regulation time, a secondary controller based on the timing theory can be designed. The controller structure is as follows:

[0153]

[0154] In the formula, u denotes the input of the secondary voltage control; c1 denotes the control parameter; V pcc denotes the power grid voltage; V nom denotes the nominal voltage of the coordinated control system; κ1 denotes a positive odd number; κ2 denotes a positive odd number; c2 denotes the control parameter.

[0155] Lemma 1: Assume the following conditions hold;

[0156] V(0) = V0;

[0157] Wherein, V represents a continuously positive definite function; represents the derivative of the continuously positive definite function; ρ1 represents a constant coefficient; ρ2 represents a constant coefficient, and it is required that ρ1 > 0 and ρ2 > 0; represents the exponent of the function V; represents the exponent of the function V; it is required that Then the nonlinear system will reach stability within a certain time, and the upper bound of the convergence time can be expressed as:

[0158]

[0159] Wherein, T represents the convergence time of the nonlinear system; T max represents the maximum convergence time of the nonlinear system; ρ1 represents a constant coefficient; ρ2 represents a constant coefficient; represents the exponent of the function V; represents the exponent of the function V.

[0160] Proof: Define the state error e as e = v pcc - v nom ;

[0161] Wherein, V pcc represents the grid-connected voltage; V nom represents the voltage reference value.

[0162] Differentiating the state error gives:

[0163]

[0164] Wherein, represents the derivative value of the state error e; represents the derivative value of the grid-connected voltage v pcc ; K dQ represents the reactive power control droop coefficient; u represents the input of the secondary voltage control; c1 represents a control parameter; κ1 represents a positive odd number; κ2 represents a positive odd number; c2 represents a control parameter.

[0165] Considering the Lyapunov function the time derivative of V can be obtained as:

[0166]

[0167] Wherein, represents the derivative of the continuously positive definite function; e represents the state error; represents the derivative value of the state error e; K dQdenotes the droop coefficient of reactive power control; c1 denotes a control parameter; κ1 denotes a positive odd number; κ2 denotes a positive odd number; c2 denotes a control parameter; α denotes a normal coefficient, and β denotes a normal coefficient, and

[0168] If e converges to 0 at time t = t0, then according to Lemma 1, it can be obtained that:

[0169]

[0170] In the formula, t0 denotes time; α denotes a normal coefficient; κ1 denotes a positive odd number; κ2 denotes a positive odd number; β denotes a normal coefficient.

[0171] It can be seen that the PCC voltage deviation e converges to 0 with a fixed upper limit of the regulation time, and this fixed time limit is related to the control parameters and is not affected by the initial state.

[0172] As Figure 2 shown, according to another embodiment of the present invention, a coordinated control method for a static var generator grid-connected renewable energy power station with active power support ability is further provided. The method includes:

[0173] S1. Simulate the external electrical characteristics of a synchronous generator, inject the active power generated by the renewable energy generation equipment into the power grid, and detect the fluctuations of the power grid voltage and frequency according to the response during the injection process;

[0174] S2. According to the power grid voltage detection result, trigger a preset voltage-reactive power droop mechanism, adjust the output of reactive power to achieve primary voltage regulation, and combine a voltage controller based on fixed-time stability to perform secondary voltage regulation;

[0175] S3. Based on the power grid frequency detection result, trigger a preset frequency-active power droop mechanism, and combine the four-quadrant operation characteristics of the static var generator to construct a virtual power channel to perform frequency regulation;

[0176] S4. Combine the results of voltage regulation and frequency regulation to coordinate the active power interaction between the virtual synchronous generator and the static var generator to achieve coordinated operation.

[0177] In summary, by means of the above technical solutions of the present invention, through the coordinated control of a static var generator with four-quadrant operation ability and a virtual synchronous generator with network-forming ability, the combined dynamic regulation of active and reactive power is achieved under a unified control framework, significantly enhancing the stable support ability of new energy power stations under grid disturbances such as voltage sags and frequency fluctuations, getting rid of the dependence on external energy storage systems, and improving the autonomous response and regulation ability of the system. By introducing the fixed-time stability theory into the voltage recovery control, the voltage recovery is completed within a predetermined time regardless of the initial disturbance conditions, significantly improving the control accuracy and fault response speed, and enhancing the adaptability and robustness of the system. By constructing a virtual power channel and introducing a dynamic power distribution mechanism, the coordinated control of active power between the VSG and the SVG is achieved, enabling the SVG to actively absorb the redundant power of the VSG during a fault, effectively alleviating the problems of energy accumulation and overvoltage on the DC side, and improving the engineering applicability and popularization value of the system.

[0178] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capability, characterized in that, The system includes: A virtual synchronous generator, which is used to simulate the external electrical characteristics of a synchronous generator and inject the active power generated by a renewable energy power generation device into the power grid; A static var generator, which is used to provide reactive power support and dynamically adjust the active power based on the four-quadrant operation characteristics when the power grid frequency fluctuates; A combined frequency and voltage regulation unit, which is used to regulate the power grid frequency and voltage and coordinately control the operating states of the virtual synchronous generator and the static var generator based on the regulation results.

2. The coordinated control system of a static var generator grid-connected renewable energy power station with active power support ability according to claim 1, characterized in that, The static var generator includes: A mathematical model construction module, which is used to collect electrical parameters based on the four-quadrant operation characteristics and construct a mathematical model of the dynamic coupling of active power and reactive power between the static var generator and the power grid based on the electrical parameters; A dynamic constraint condition setting module, which is used to calculate the maximum active power output by the static var generator according to the maximum current limit of the static var generator, combined with the output voltage of the energy storage converter and the power grid current, and set the maximum active power as the corresponding dynamic constraint condition; A state detection module, which is used to detect the fluctuation changes of the power grid voltage and the power grid frequency.

3. A coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capability according to claim 2, characterized in that, The expression of the mathematical model is: where P represents the active power of the static var generator; V svg represents the output voltage of the static var generator; V pcc represents the grid voltage; δ represents the angle between the output voltage of the static var generator and the grid voltage; Q represents the reactive power of the static var generator; ω represents the grid angular velocity; L represents the value of the filtering inductor; The expression of the dynamic constraint condition is: Wherein, P max represents the maximum active power output by the static var generator; Q represents the reactive power of the static var generator; V ap represents the output voltage of the energy storage part of the static var generator; V pcc represents the grid voltage.

4. A coordinated control system for a static var generator grid-connected renewable energy power station with active power support ability according to claim 1, characterized in that, The combined frequency and voltage regulation unit includes: A voltage droop control module, which is used to trigger a preset voltage-reactive power droop mechanism according to the power grid voltage detection result, adjust the output of reactive power to achieve primary voltage regulation, and perform secondary voltage regulation in combination with a voltage controller based on fixed-time stability; A frequency droop control module, which is used to trigger a preset frequency-active power droop mechanism based on the power grid frequency detection result and construct a virtual power channel in combination with the four-quadrant operation characteristics of the static var generator to perform frequency regulation.

5. A coordinated control system for a static var generator grid-connected renewable energy power station with active power support capability according to claim 4, characterized in that The expression of the voltage-reactive power droop mechanism is: V ref -V pcc = K dQ (Q ref - Q0); Wherein, V ref represents the voltage reference value; V pcc represents the grid voltage; K dQ represents the droop coefficient of reactive power control; Q′ ref represents the reactive power reference value generated by droop control; Q0 represents the reactive power base value of the static var generator; The expression of the frequency-active power droop mechanism is: f ref -f = K dP (P - P0); where f ref represents the frequency reference value; f represents the frequency; K dP represents the droop coefficient of active power control; P represents the active power of the static var generator; P0 represents the base value of the active power of the static var generator.

6. A coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capability, characterized in that, The voltage droop control module includes: A primary voltage regulation sub-module, which is used to when it detects that the power grid voltage drops, the static var generator triggers a preset voltage-reactive power droop mechanism according to the voltage deviation degree, calculates the initial reactive power reference value, and injects the corresponding reactive power to achieve primary voltage regulation; A secondary voltage regulation sub-module, which is used to design a voltage controller based on the fixed-time stability theory according to the result of the primary voltage regulation and perform secondary voltage regulation to correct the voltage deviation.

7. A coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capability, characterized in that, The expression of the voltage controller is: where u represents the input of secondary voltage control; c1 represents a control parameter; V pcc represents the grid voltage; V nom represents the nominal voltage of the coordinated control system; κ1 represents a positive odd number; κ2 represents a positive odd number; c2 represents a control parameter.

8. A coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capability, characterized in that, The frequency droop control module includes: An active power adjustment sub-module, which is used to when it detects that the power grid frequency drops, the static var generator triggers a preset frequency-active power droop mechanism according to the frequency deviation degree and calculates the active power reference value in combination with a fast frequency response framework to adjust the output of active power; A virtual power channel construction sub-module, which is used to construct a virtual power channel between the static var generator and the virtual synchronous generator in combination with the active power adjustment result and the four-quadrant operation characteristics of the static var generator; A frequency regulation sub-module, which is used to dynamically absorb the active power output by the virtual synchronous generator while the static var generator outputs reactive power to support the voltage based on the constructed virtual power channel, so as to achieve frequency regulation between the virtual synchronous generator and the static var generator.

9. A coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capability, characterized in that, The expression for the static var generator to dynamically absorb the active power output by the virtual synchronous generator while outputting reactive power to support the voltage is: Where, P APSC-SVG represents the active power of the static var generator; P max represents the maximum active power output by the static var generator; P VSG represents the active power of the virtual synchronous generator.

10. A coordinated control method for a grid-connected renewable energy power station with a static var generator having active power support capability, which uses the coordinated control system for a grid-connected renewable energy power station with a static var generator having active power support capability described in any one of claims 1-9, characterized in that, The method includes: S1. Simulate the external electrical characteristics of the synchronous generator, inject the active power generated by the renewable energy power generation equipment into the power grid, and detect the fluctuations of the grid voltage and frequency according to the response during the injection process; S2. According to the grid voltage detection result, trigger the preset voltage-reactive power droop mechanism, adjust the output of reactive power to achieve primary voltage regulation, and combine with the voltage controller based on fixed-time stability to perform secondary voltage regulation; S3. Based on the grid frequency detection result, trigger the preset frequency-active power droop mechanism, and combine with the four-quadrant operation characteristics of the static var generator to construct a virtual power channel and perform frequency regulation; S4. Combine the results of voltage regulation and frequency regulation, and coordinate the active power interaction between the virtual synchronous generator and the static var generator to achieve coordinated operation.

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