Three-parameter coordinated adaptive control method for energy storage converter based on VSG

Abstract

The invention discloses a VSG-based energy storage converter three-parameter coordinated adaptive control method, which comprises the following steps of: acquiring three-phase voltage and current of a VSG output port and three-phase voltage data of a grid-connected point, and calculating an output power difference, an output power change rate and a power grid angular frequency difference of the VSG; the power instruction is corrected by combining the power instruction and the power grid angular frequency difference, and the adjustment process of the VSG is divided into six stages according to a power fluctuation curve; the rotational inertia, the virtual damping and the virtual inductance are adjusted according to the power difference and the power change rate in the six stages; the virtual inductor is finely adjusted by combining the VSG output power difference and the output power change rate, and smooth transition of the virtual inductor and smooth adjustment of the power are achieved; the value of the virtual inductance is compared with the initial value of the virtual inductance, and the virtual impedance is subjected to initial value regression operation, so that the power equalization and the system stability of the parallel VSG are not influenced. The method has obvious effects on power oscillation suppression and dynamic performance improvement of the energy storage converter system based on the VSG.

Description

Technical Field

[0001] The present invention relates to the technical field of power oscillation suppression of a grid-connected energy storage converter, and in particular to a three-parameter coordinated adaptive control method of an energy storage converter based on a VSG. Background Art

[0002] VSG-based energy storage converters play an important role in modern power systems, especially in renewable energy integration and grid regulation. With the rapid development of renewable energy such as wind and solar energy, the demand for efficient and flexible energy storage systems is increasing. VSG technology, with its superior power conversion capability and dynamic response performance, has become the key to achieving grid frequency and voltage support. A large number of studies are being devoted to optimizing its control strategy, improving system reliability and safety, and exploring integrated applications with various energy storage technologies such as batteries and supercapacitors. In addition, global policy push for renewable energy is also accelerating the development of this field. Future research will focus on improving control algorithms, material innovation, and the collaborative work of VSG and other power electronic devices to meet the growing demand for electricity and sustainable development goals.

[0003] VSG (Virtual Synchronous Generator) power oscillation suppression technology is an area that has gradually attracted attention in the integration of smart power and renewable energy in recent years. With the rapid development of renewable energy (such as wind power and solar power), traditional generators are gradually being replaced, and the dynamic characteristics and stability of power systems are facing new challenges.

[0004] Traditional power systems rely on rotating generators that provide inertia and damping in the grid to help maintain system stability. However, with the access of renewable energy sources, especially those based on power electronic converters (such as wind power and photovoltaics), the inertia and damping characteristics of the system have changed significantly. There are many forms of power oscillations (such as low-frequency oscillations) in the power system, which can affect the stability of the system and even cause it to collapse. The access of renewable energy sources may make these oscillations more obvious, especially when there are changes in grid load and fluctuations in renewable energy generation.

[0005] VSG is a control strategy that simulates the characteristics of traditional synchronous generators and is designed to enhance the stability of power electronics-based power generation equipment (such as inverters) in the power grid. VSG can provide inertia and damping characteristics similar to traditional generators by controlling the relationship between its output power and the grid frequency. VSG is usually implemented through control system design, which includes appropriate control strategies for power electronic devices, such as frequency response, power factor control, etc., to improve the dynamic performance of the system. At the same time, VSG can also further improve the stability of the system by coordinating with other grid equipment (such as energy storage systems).

[0006] Research on VSG power oscillation suppression technology will not only help improve the stability of the power system, but also help promote the widespread application of renewable energy and promote the transformation and upgrading of the energy structure. In addition, the application of VSG technology can also improve the flexibility and reliability of the power grid and support a higher proportion of renewable energy access.

[0007] The traditional parameter adaptive control strategy uses adaptive virtual damping and adaptive rotational inertia methods to modify the damping of the system, but its control effect is very limited, and there is a contradiction between its power oscillation suppression effect and power response speed. For large-capacity power grids, its output adjustment speed affects the stability of the power grid to a certain extent. Summary of the invention

[0008] The technical problem to be solved by the present invention is to address the contradiction between VSG power oscillation and power response speed, and propose a coordinated adaptive control strategy of virtual moment of inertia, virtual damping and virtual inductance. Since the size of the virtual impedance directly affects the amplitude and phase of the virtual output voltage, and thus affects the output power, its impact on the power response is faster, but also more complex. The invention can improve the effect of VSG power oscillation suppression and the dynamic performance of the system by coordinated adaptive control of the three parameters of moment of inertia, virtual damping and virtual inductance.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] The present invention provides a three-parameter coordinated adaptive control method for an energy storage converter based on a VSG, the method comprising the following steps:

[0011] S1: Add a virtual impedance in the virtual synchronous generator system, wherein the virtual impedance includes a virtual inductor and a virtual resistor; collect three-phase voltage and current data of the VSG output port and the grid connection point, and calculate the VSG output power difference, power change rate and angular frequency difference;

[0012] S2: The power command is corrected by combining the power command and the grid angular frequency difference, the angular frequency oscillation curve is replaced by the power oscillation curve, and the oscillation process of the VSG output power is divided into 6 stages based on the power difference and the power change rate;

[0013] S3: Calculate and adjust the moment of inertia, virtual damping and virtual inductance in 6 stages;

[0014] S4: Detect the VSG output power difference and power change rate in 6 stages. When the power adjustment direction deviates from the corrected power command, readjust the virtual inductance based on the original control strategy to suppress the power deviation. Then detect whether the value of the virtual inductance deviates from the initial value. If it deviates from the initial value, compensate the virtual inductance with a small step to adjust the virtual inductance to the initial value.

[0015] S5: Analyze the output impedance characteristics of the system through the transfer function of the output impedance, determine the value of the virtual resistance according to the variation range of the virtual impedance; and determine the selected virtual impedance according to the determined virtual inductance and virtual resistance.

[0016] Furthermore, the virtual synchronous generator system of the present invention comprises a system main circuit and a control circuit connected to each other; wherein:

[0017] The main circuit of the system includes a DC power supply, a three-phase inverter bridge arm and an LCL filter connected in sequence;

[0018] The control circuit comprises a power outer loop, a voltage-current double closed loop and a PWM modulation part which are connected in sequence; a virtual impedance for power decoupling and power oscillation suppression is added to the voltage-current double closed loop.

[0019] Furthermore, the specific steps in S1 of the present invention are:

[0020] S11: Collect and record the three-phase voltage and current data of the VSG output port and the grid connection point at each moment during operation;

[0021] S12: Perform clack transformation on the voltage and current output by the VSG, and calculate the active and reactive power output by the VSG in the α and β coordinate systems:

[0022]

[0023] Among them: U A , U B , U C is the three-phase voltage output by VSG; U α , U β P is the voltage of the VSG output three-phase voltage after clack transformation; e and Q e It is the active and reactive power output of VSG;

[0024] S13: Calculate the angular frequency of the VSG output voltage and the grid common connection point voltage using a phase-locked loop.

[0025] Furthermore, the specific steps in S2 of the present invention are:

[0026] S21: Use the VSG output voltage angular frequency and the grid voltage angular frequency to correct the power command, where P set is the initial active power instruction of VSG; P set ' is the corrected active power instruction; D p is the active droop coefficient, i.e. the damping coefficient; ω o is the angular frequency of the VSG output voltage; ω g is the angular frequency of the grid-connected point voltage;

[0027] P set '=P set +D p (ω o -ω g )

[0028] S21: Determine the demarcation point between the VSG power oscillation stages according to the corrected power command, power difference and power change rate, P u , P d are the upper and lower limits of the power reference threshold respectively; ΔP ω is the power increase of primary frequency modulation; ΔP s is the amplitude of low-frequency oscillation of output power of VSG in steady state;

[0029]

[0030]

[0031] S22: The upper and lower limits of the power reference threshold and the power oscillation curve form at most four intersection points, namely, the dividing points of the oscillation cycle. According to the four dividing points and the extreme points of the oscillation cycle, one cycle of the power oscillation curve is divided into six stages:

[0032]

[0033] Where: P e is the electromagnetic power output by VSG;

[0034] The VSG output power is divided into the following parts according to time in one oscillation cycle:

[0035]

[0036] Among them: t1~t7 are the times corresponding to each dividing point in one oscillation cycle.

[0037] Furthermore, the specific steps in S3 of the present invention are:

[0038] S31: The damping coefficient of VSG and the size of virtual rotation inertia will affect the damping of the system. According to the relationship between the system damping, the damping coefficient and the virtual rotation inertia, the virtual rotation inertia J is reduced when the VSG output power approaches the corrected power command, and the virtual rotation inertia J is increased when the VSG output power moves away from the corrected power command to adjust the virtual rotation inertia.

[0039]

[0040]

[0041]

[0042] Where: T m is the input torque of the prime mover, T e is the electromagnetic torque of VSG, ω is the angular frequency of VSG output voltage, ω n is the rated angular frequency, D p is the active droop coefficient, i.e., the damping coefficient, J0 is the initial value of the virtual moment of inertia, and J1 is the original output value of the virtual moment of inertia;

[0043] S32: Similarly, the virtual damping is adjusted according to the rule that the virtual damping D is reduced when the VSG output power approaches the corrected power command and the virtual damping D is increased when the VSG output power moves away from the corrected power command;

[0044]

[0045] Where: D p0 is the initial value of the damping coefficient, D p1 is the original output value of the virtual impedance;

[0046] S33: The size of the virtual inductor will affect the amplitude and phase of the output voltage, but under power closed-loop control, the voltage amplitude and phase given by the voltage and current dual closed-loop will be compensated. The larger the virtual inductor is, the greater the impact on the output voltage and the greater the degree of system compensation. Therefore, the addition of the virtual inductor is equivalent to adding additional damping to the system. Similarly, the virtual inductor is adjusted according to the rule that the virtual inductance L is reduced when the VSG output power approaches the corrected power instruction and the virtual inductance L is increased when the VSG output power moves away from the corrected power instruction.

[0047]

[0048] Where: k1 and k2 are the adjustment coefficients of power change rate and power difference to virtual inductance respectively; L v0 is the initial value of the corrected virtual inductance, L v1is the initial output value of the main part of the virtual inductor; when the system is in a transition state, L v1 Maintain the original value and avoid frequently adjusting the value of the virtual inductance near the transition state.

[0049] Furthermore, the specific steps in S4 of the present invention are:

[0050] S41: Compensate the power command when the grid frequency is offset, and obtain the corrected power command as follows:

[0051] P set '=P set +D p (ω n -ω g )

[0052] S42: When the grid frequency deviates, the amplitude of the power oscillation is often larger than when the power command changes, so the initial value of the virtual inductance is compensated:

[0053]

[0054] Where: L v0 is the initial value of the corrected virtual inductance. L base is the basic value of virtual impedance; ω g is the grid angular frequency;

[0055] S42: The virtual inductor adopts an adaptive adjustment method. Its adjustment process will cause the amplitude and phase of the output voltage to change. Therefore, during the power adjustment process, the virtual inductor is fine-tuned in the opposite direction when the output power moves away from the target power according to the change trend of the output power, so as to reduce the fluctuation of the output power:

[0056]

[0057] Where: L v2(n) is the value of the virtual inductance fine-tuning part of the current sampling period; L v2(n-1) is the value of the virtual inductance fine-tuning part in the previous sampling cycle; ΔL1 and ΔL2 are the period adjustment values ​​of the virtual inductance fine-tuning part;

[0058] S43: The virtual circuit is divided into two parts, where L v1 is the main part of the virtual inductor, L v2(n) It is the fine-tuning part of the virtual inductor. At the same time, in order to ensure the smooth transition of the virtual inductor, its output is connected to a low-pass filter, that is:

[0059]

[0060] S44: To ensure power sharing in parallel with VSG, L v2(n-1)In steady state, the virtual inductance returns to the initial value, and is continuously adjusted to the initial value during the adjustment process of the virtual inductance, that is, when the virtual inductance deviates from the initial value, a small adjustment value is added or subtracted, where ΔL3 is the periodic adjustment value of the virtual inductance returning to the initial value:

[0061]

[0062] S45: In order for the fine-tuning part of the virtual impedance to work properly, the three periodic adjustment values ​​of the virtual impedance meet the following requirements:

[0063] ΔL1>ΔL3>ΔL2.

[0064] Furthermore, the specific steps in S5 of the present invention are:

[0065] S51: In order to improve the response speed of the system, an output voltage feedforward link is added to the voltage-current double closed loop, and the voltage loop closed loop transfer function is as follows:

[0066]

[0067] Where: G I is the proportional controller of the current loop; L1 and R1 are the inductance and resistance of the filter on the far grid side respectively; C is the filter capacitor in the LCL filter; k p , k i are the proportional coefficient and integral coefficient of the voltage loop PI controller respectively; in VSG, the additional resistance R1 on the filter inductor L1 in the filter is much smaller than the inductor L1, so R1 is treated as 0;

[0068] S52: The total impedance between VSG and the grid connection point after adding the virtual impedance is obtained from the voltage loop transfer function as follows:

[0069] Z' o (s) = Z o (s)+G b2 (s)·(R v +sL v )+Z2

[0070] Where: Z2 is the line impedance, Z o is the output impedance of VSG; Z2 is the line impedance between VSG and the grid connection point;

[0071] S53: Based on the transfer function of the total output impedance, draw the Bode diagram of the total output impedance under different virtual resistances, and take the virtual resistance as the value of the output impedance that is closest to the pure inductance characteristic.

[0072] The present invention provides a VSG-based energy storage converter three-parameter coordinated adaptive control system, comprising:

[0073] a memory for storing executable computer programs;

[0074] The processor is used to implement the above-mentioned VSG-based three-parameter coordinated adaptive control method of energy storage converter when executing the executable computer program stored in the memory.

[0075] Compared with the existing VSG power oscillation suppression technology, the beneficial effects of the present invention are:

[0076] 1. The traditional control algorithm using fixed virtual impedance cannot take into account both the effect of power oscillation suppression and the speed of power response. Compared with the existing adaptive and improved fuzzy adaptive control algorithms, the three-parameter coordinated adaptive control method of energy storage converter based on VSG proposed in this invention introduces adaptive virtual inductance L into the existing control strategy. v , which has obvious effects on suppressing power oscillation and improving response speed.

[0077] 2. The three-parameter coordinated adaptive control method of the energy storage converter based on VSG proposed in the present invention has a good suppressing effect on the power oscillation when the system power and frequency change, and the proposed control algorithm has stronger applicability.

[0078] 3. The present invention uses power difference, power change rate and frequency difference as feedback parameters. Compared with the traditional control strategy by detecting angular frequency, the present invention directly operates power, and the response speed of the system and the accuracy of the control strategy action are greatly improved.

[0079] In summary, the coordinated adaptive strategy of adaptive virtual moment of inertia, virtual damping and virtual inductance adopted in the present invention can obtain a larger feasible domain through the coordination of three parameters, and it has a certain improvement in the suppression of power oscillation and the speed of power response, and it also has a very obvious effect on improving the stability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0081] Figure 1 It is a schematic diagram of the overall structure of the virtual synchronous generator of the present invention;

[0082] Figure 2 It is a block diagram of voltage and current double closed-loop control with voltage feedforward in the present invention;

[0083] Figure 3 is a diagram showing the relationship between the virtual inductance, line inductance and VSG output impedance in the present invention; (a) L v and the relationship between L2 and the output impedance angle; (b) L v and the relationship between L2 and the output impedance amplitude;

[0084] Figure 4 The damping mechanism diagram of the virtual impedance in the present invention; (a) containing the virtual impedance Z v VSG control structure diagram; (b) including virtual impedance Z v VSG output voltage vector diagram;

[0085] Figure 5 It is a diagram of the power oscillation phase in the present invention;

[0086] Figure 6 is the output impedance Bode diagram under different virtual resistances in the present invention;

[0087] Figure 7 It is a structural diagram of the three-parameter coordinated adaptive control method of the energy storage converter based on VSG in the present invention;

[0088] Figure 8 When the active power command is adjusted from 0kW to 10kW at t=0.5s, the power response curves of the adaptive control policies (ACP) and the three-parameter coordinated adaptive control method of the energy storage converter based on VSG under different virtual inductances; (a) active power; (b) reactive power;

[0089] Fig. 9 When the active power command is adjusted from 0kW to 10kW at t=0.5s, the power response curves of the fuzzy adaptive control strategy under different virtual inductances and the three-parameter coordinated adaptive control method of the energy storage converter based on VSG; (a) active power; (b) reactive power;

[0090] Fig.10 When the active power command is adjusted from 0kW to 10kW at t=0.5s, the power response curves of the adaptive control policies (ACP) and the three-parameter coordinated adaptive control method of the energy storage converter based on VSG under different virtual inductances; (a) active power; (b) reactive power;

[0091] Fig.11 When the active power command is adjusted from 0kW to 10kW at t=0.5s, the power response curves of the fuzzy adaptive control strategy under different virtual inductances and the three-parameter coordinated adaptive control method of the energy storage converter based on VSG; (a) active power; (b) reactive power. DETAILED DESCRIPTION

[0092] In order to better understand the inventive method, the following is a complete and clear description of the principles and features of the present invention in conjunction with the accompanying drawings. The examples given are only used to explain the present invention so that those skilled in the art can implement it according to the implementation scheme. The present invention can be implemented in various forms and is not limited to the specific implementation scheme. All other examples obtained by ordinary technicians without any creative work on the invention belong to the protection scope of the present invention.

[0093] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0094] The terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance. In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, and it can be the internal connection of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0095] like Figure 1 As shown in the figure, the main circuit of the system consists of a DC power supply, a three-phase inverter bridge arm and an LCL filter, wherein the LCL filter is composed of the LC filter, C and line inductance. The control circuit is mainly composed of a power outer loop, a voltage and current double closed loop and a PWM modulation part. The traditional VSG power oscillation suppression strategy suppresses power oscillation by modifying the virtual moment of inertia and virtual damping of the power loop, but the relationship between the virtual moment of inertia and virtual damping and the angular frequency change rate of the VSG output voltage is coupled. Therefore, when suppressing power oscillation, the method of increasing transient damping is often used, but this will cause a significant decrease in the power response speed of the system.

[0096] like Figure 2 As shown, adding a virtual impedance in the voltage-current double closed loop is not only beneficial to power decoupling, but also can suppress power oscillation to a certain extent.

[0097] like Figure 3 As shown in the figure, the influence trends of virtual inductance and line inductance on the total output impedance of VSG are consistent. Therefore, adding inductance is beneficial to the decoupling control of power. However, excessive virtual inductance will also increase the damping of the system, thereby affecting the response speed of the system output power.

[0098] like Figure 4As shown, when the active power command P set When the VSG power ring output voltage E ref The phase angle increases. Under this power instruction, the theoretical final value of the output voltage of VSG is u o2 However, during the adjustment process, the voltage drop on the grid-connected line gradually increases, and its output current i o The voltage drop on the virtual impedance also increases gradually. The voltage set value U of the voltage-current double closed loop ref is less than the expected value, the VSG output voltage is at u o1 with u o2 u between o12 , although the power outer loop adjusts E ref The phase can achieve active differential regulation, but compared with the VSG control strategy without virtual impedance, its E ref The phase that needs to be adjusted is larger and the adjustment time required is longer. Similarly, when the reactive power command increases, the VSG power loop output voltage E ref The amplitude of increases. Under this reactive power instruction, the theoretical final value of the output voltage of VSG is u o3 However, during the adjustment process, the voltage drop on the grid-connected line gradually increases, and its output current i o The voltage drop on the virtual impedance also increases gradually. The voltage set value U of the voltage-current double closed loop ref Less than the expected value, under this condition, the VSG output voltage is u o1 and u o3 u between o13 Although the reactive power can be regulated without difference under the regulation of the power outer loop, its E ref The amplitude that needs to be adjusted is larger and the adjustment time is longer. Conversely, the same is true when the active and reactive power instructions decrease.

[0099] Depend on Figure 4 It can be seen that when the virtual impedance changes, the voltage amplitude and phase of the system output will change suddenly, and from the output expressions of active and reactive power, it can be seen that the amplitude and phase of the VSG output voltage directly affect the active and reactive power output of the system. Therefore, using the traditional adaptive control strategy to control the virtual impedance will cause the system power to oscillate repeatedly during the adjustment process, and even its oscillation amplitude will exceed the amplitude when the power oscillation suppression strategy is not adopted. In the present invention, the virtual impedance is divided into two parts: virtual inductance and virtual resistance for design. The virtual inductance is divided into two parts. The first part L v1 To provide a general trend for the adjustment of virtual inductance, the second part L v2(n)By detecting the change trend of VSG output power, the virtual inductance is adjusted to achieve smooth transition of virtual inductance and smooth control of VSG output power. Therefore, the addition of virtual impedance has the effect of suppressing the rate of change of output voltage phase and amplitude, and there is no coupling relationship between virtual impedance and virtual moment of inertia and virtual damping. Selecting an appropriate way to adjust virtual impedance can be used as a strategy to suppress power oscillation and optimize system dynamic performance.

[0100] like Figure 5 As shown in the figure, after the system parameters are determined, the value of the virtual resistance also has a certain influence on the damping of the system, but it mainly affects the degree of coupling between the active and reactive power of the system. When the virtual resistance is too large, the resistive part of the output impedance of the system is too large, which is contrary to the strategy of VSG power decoupling control and is not conducive to the stability of the system; when the virtual resistance is too small, the output impedance of the system presents a negative resistance characteristic in the low frequency band, and as the virtual resistance value further decreases, the negative resistance characteristic of the output impedance gradually shifts to the high frequency, so the value of the virtual resistance is moderate.

[0101] like Figure 6 As shown, P u , P d are the upper and lower limits of the power reference threshold respectively; t1~t7 are the time of the six stage dividing points. In the figure, the system is in the process of adjusting the output power to the steady-state value in stage 1 and stage 4. At this time, there is a large difference between the VSG output power and the steady-state value, and the system damping should be reduced; when the system is in stage 2 and stage 5, the difference between the VSG output power and the steady-state power is small, and the system damping should be increased to prevent power overshoot; in stage 3 and stage 6, the VSG output power difference gradually increases, and the system damping should be increased to suppress the amplitude of power overshoot.

[0102] In summary, in order to suppress the power oscillation of VSG, the present invention adopts a three-parameter coordinated adaptive control method of VSG-based energy storage converter with virtual rotation inertia, virtual damping and virtual inductance. Figure 7 As shown, the following steps are included:

[0103] S1: Collect the three-phase voltage and current data of the VSG output port and the grid connection point, and calculate the VSG output power difference, output power change rate and angular frequency difference;

[0104] S2: The power command is corrected by combining the power command and the grid angular frequency difference, the angular frequency oscillation curve is replaced by the power oscillation curve, and the oscillation process of the VSG output power is divided into 6 stages based on the power difference and the power change rate;

[0105] S3: The moment of inertia, virtual damping and virtual inductance are adjusted in 6 stages.

[0106] S4: The VSG output power difference and power change rate are detected in 6 stages. When the power adjustment direction deviates from the corrected power instruction, the virtual inductance is readjusted based on the original control strategy to suppress the power deviation; then the value of the virtual inductance is detected to see if it deviates from the initial value. If it deviates from the initial value, the virtual inductance is compensated for with a small step size to adjust the virtual inductance to the initial value.

[0107] S5: Analyze the output impedance characteristics of the system through the transfer function of the output impedance, and select a suitable virtual negative resistance based on the requirements of power decoupling control of the energy storage converter.

[0108] The specific steps in S1 are:

[0109] S11: Collect and record the three-phase voltage and current data of the output port and the grid connection point of the energy storage converter at each moment during operation;

[0110] S12: Perform clack transformation on the voltage and current output by VSG, and calculate the active and reactive power output by VSG in the α and β coordinate systems, where U A , U B , U C is the three-phase voltage output by VSG; U α , U β P is the voltage of the VSG output three-phase voltage after clack transformation; e and Q e It is the active and reactive power output by VSG.

[0111]

[0112]

[0113] S13: Calculate the angular frequency of the VSG output voltage and the grid common connection point voltage using a phase-locked loop.

[0114] The specific steps in S2 are:

[0115] S21: Use the VSG output voltage angular frequency and the grid voltage angular frequency to correct the power command, where P set is the initial active power instruction of VSG; P set ' is the corrected active power instruction; D p is the active droop coefficient, i.e. the damping coefficient; ω o is the angular frequency of the VSG output voltage; ω g is the angular frequency of the grid-connected point voltage.

[0116] P set '=P set +D p (ω o-ω g ) (3)

[0117] S21: Determine the demarcation point between the VSG power oscillation stages according to the corrected power command, power difference and power change rate, P u , P d are the upper and lower limits of the power reference threshold respectively; ΔP ω is the power increase of primary frequency modulation; ΔP s is the amplitude of low-frequency oscillation of output power of VSG in steady state.

[0118]

[0119]

[0120] S22: The upper and lower limits of the power reference threshold and the power oscillation curve can form at most 4 intersection points, i.e., the dividing points of the oscillation cycle. According to the 4 dividing points and the extreme points of the oscillation cycle, one cycle of the power oscillation curve can be divided into 6 stages, where P e is the electromagnetic power output by VSG.

[0121]

[0122] The VSG output power can be divided into the following according to time in one oscillation cycle: t1~t7 are the times corresponding to the various dividing points in one oscillation cycle:

[0123]

[0124] The specific steps in S3 are:

[0125] S31: The damping coefficient of VSG and the size of virtual rotation inertia will affect the damping of the system. According to the relationship between the system damping, damping coefficient and virtual rotation inertia, the virtual rotation inertia J is reduced when the VSG output power approaches the corrected power instruction and the virtual rotation inertia J is increased when the VSG output power is far from the corrected power instruction. The virtual rotation inertia is adjusted according to the rule, where T m is the input torque of the prime mover, T e is the electromagnetic torque of VSG, ω is the angular frequency of VSG output voltage, ω n is the rated angular frequency, D p is the active droop coefficient, i.e., the damping coefficient, J0 is the initial value of the virtual moment of inertia, and J1 is the original output value of the virtual moment of inertia;

[0126]

[0127]

[0128]

[0129] S32: Similarly, the virtual damping is adjusted according to the rule that the virtual damping D is reduced when the VSG output power approaches the corrected power instruction and the virtual damping D is increased when the VSG output power moves away from the corrected power instruction, where D p0 is the initial value of the damping coefficient, D p1 is the original output value of the virtual impedance;

[0130]

[0131] S33: The size of the virtual inductor will affect the amplitude and phase of the output voltage, but under power closed-loop control, it will compensate for the voltage amplitude and phase given by the voltage and current dual closed-loops. The larger the virtual inductance, the greater the impact on the output voltage and the greater the degree of system compensation. Therefore, the addition of virtual inductance is equivalent to adding additional damping to the system. Similarly, the virtual inductance is adjusted according to the rule that the virtual inductance L is reduced as the VSG output power approaches the corrected power instruction and the virtual inductance L is increased as the VSG output power moves away from the corrected power instruction. Among them: k1 and k2 are the adjustment coefficients of the power change rate and power difference on the virtual inductance respectively; L v0 is the initial value of the corrected virtual inductance, L v1 is the initial output value of the main part of the virtual inductor. When the system is in the transition state, L v1 Maintain the original value and avoid frequently adjusting the value of the virtual inductance near the transition state.

[0132]

[0133] The specific steps in S4 are:

[0134] S41: Compensate the power command when the grid frequency is offset, and obtain the corrected power command as follows:

[0135] P set '=P set +D p (ω n -ω g ) (13)

[0136] S42: When the grid frequency deviates, the amplitude of power oscillation is often larger than when the power command changes. Therefore, it is necessary to compensate the initial value of the virtual inductance, where L v0 is the initial value of the corrected virtual inductance. L base is the basic value of virtual impedance; ω g is the grid angular frequency.

[0137]

[0138] S42: The virtual inductor in the present invention adopts an adaptive adjustment method, and its adjustment process will cause the amplitude and phase of the output voltage to change. Therefore, in the process of power adjustment, it is necessary to adjust the virtual inductor in the opposite direction according to the change trend of the output power when the output power moves away from the target power, so as to reduce the fluctuation of the output power. Wherein: L v2(n) is the value of the virtual inductance fine-tuning part of the current sampling period; L v2(n-1) is the value of the virtual inductance fine-tuning part in the previous sampling period; ΔL1 and ΔL2 are the period adjustment values ​​of the virtual inductance fine-tuning part.

[0139]

[0140] S43: The present invention divides virtual electricity into two parts, wherein L v1 is the main part of the virtual inductor, L v2(n) It is the fine-tuning part of the virtual inductor. To ensure the smooth transition of the virtual inductor, its output needs to be connected to a low-pass filter, that is:

[0141]

[0142] S44: To ensure power sharing in parallel with VSG, L v2(n-1) It needs to return to the initial value in steady state. Therefore, it is necessary to continuously adjust the virtual inductance to the initial value during the adjustment process. That is, when the virtual inductance deviates from the initial value, a small adjustment value is added or subtracted, where ΔL3 is the periodic adjustment value of the virtual inductance returning to the initial value.

[0143]

[0144] S45: In order for the fine-tuning part of the virtual impedance to work properly, the three periodic adjustment values ​​of the virtual impedance must meet the following requirements:

[0145] ΔL1>ΔL3>ΔL2 (18)

[0146] The specific steps in S5 are:

[0147] S51: In order to improve the response speed of the system, an output voltage feedforward link is added to the voltage and current double closed loop, and the voltage loop closed loop transfer function is as follows, where G I is the proportional controller of the current loop; L1 and R1 are the inductance and resistance of the filter on the far grid side respectively; C is the filter capacitor in the LCL filter; k p , k i They are the proportional coefficient and integral coefficient of the voltage loop PI controller respectively. In VSG, the additional resistance R1 on the filter inductor L1 in the filter is generally very small and much smaller than the inductor L1, so R1 can be treated as 0;

[0148]

[0149] S52: The total impedance between VSG and the grid connection point after adding virtual impedance is obtained from the voltage loop transfer function as follows, where Z2 is the line impedance, Z o is the output impedance of VSG; Z2 is the line impedance between VSG and the grid connection point;

[0150] Z' o (s) = Z o (s)+G b2 (s)·(R v +sL v )+Z2 (20)

[0151] S53: Based on the transfer function of the total output impedance, draw the Bode diagram of the total output impedance under different virtual resistances, and take the virtual resistance as the value of the output impedance that is closest to the pure inductance characteristic.

[0152] In order to verify the effectiveness of the method described in the present invention in suppressing output power oscillation and improving power response speed, models of a 10 kV·A adaptive control strategy, a fuzzy control strategy and a three-parameter coordinated adaptive control method of a VSG-based energy storage converter were built respectively.

[0153] Figure 8 When t=0.5s, the active power command is adjusted from 0kW to 10kW, and the power response curves of the adaptive control policies (ACP) and JDL coordinated control strategies under different virtual inductances. Fig. 9 When t=0.5s, the active power command is adjusted from 0kW to 10kW. The power response curves of the fuzzy adaptive control strategy under different virtual inductances and the three-parameter coordinated adaptive control method of the energy storage converter based on VSG are shown.

[0154] Depend on Figure 8 and Fig. 9It can be seen that when the value of virtual inductance is set to 1mH, 3mH, and 6mH, the time for the power to adjust to steady state using the adaptive control strategy is 0.18s, 0.2s, and 0.25s, respectively, and the active power overshoot is 17%, 12%, and 5%, respectively, and the fluctuation amplitude of reactive power is 811var, 551var, and 554var, respectively. The time for the power to adjust to steady state using the fuzzy adaptive control strategy is 0.2s, 0.22s, and 0.23s, respectively, and the active power overshoot is 19%, 14%, and 4%, respectively, and the fluctuation amplitude of reactive power is 911var, 497var, and 581var, respectively. Compared with the adaptive control strategy of fixed virtual impedance and the fuzzy adaptive control strategy, the active power of the three-parameter coordinated adaptive control method of the energy storage converter based on VSG proposed in the present invention reaches near the steady-state value within 0.1s, and its active power overshoot is less than 5%, and the reactive power fluctuation amplitude is equivalent to the overshoot when the virtual inductance is 1mH under the fuzzy control strategy, but the time when the reactive power is affected is less than 0.1s.

[0155] Fig.10 and Fig.11 They are the power response curves of the grid frequency dropping from 50Hz to 49Hz at t=0.5s, using ACP and a three-parameter coordinated adaptive control method of energy storage converter based on VSG, and using a fuzzy control strategy and a three-parameter coordinated adaptive control method of energy storage converter based on VSG.

[0156] Depend on Fig.10 and Fig.11 It can be seen that compared with power disturbance, frequency disturbance has a more obvious impact on system power stability. Under frequency disturbance, the influence trend of virtual inductance on power oscillation suppression is consistent with the influence trend of power disturbance on power oscillation suppression. When the virtual inductance of VSG is set to 1mH, 3mH and 6mH respectively, the active power overshoot of the adaptive control strategy is 60%, 40% and 24% respectively, and the reactive power fluctuation amplitude is 3312var, 1583var and 1214var respectively. The time to reach steady state is 0.17s, 0.23s and 0.24s respectively; the active power overshoot of the improved fuzzy adaptive control strategy is 70%, 44% and 26% respectively, the reactive power fluctuation amplitude is 3337var, 1672var and 1408var respectively, and the time to reach steady state is 0.17s, 0.23s and 0.25s respectively. The active power overshoot of the VSG-based energy storage converter three-parameter coordinated adaptive control method proposed in the present invention is 5%, the reactive power fluctuation amplitude is 2989 var, and the time for adjusting to the steady state is 0.15 s.

[0157] From the above examples, it can be seen that when the system is subjected to a power disturbance of 100% capacity and a frequency disturbance of 1Hz, the VSG-based energy storage converter three-parameter coordinated adaptive control method proposed in the present invention can effectively suppress power oscillations. Similarly, when the power command decreases and the grid frequency increases, the VSG-based energy storage converter three-parameter coordinated adaptive control method proposed in the present invention can improve the effect of power oscillation suppression and the dynamic performance of the system.

[0158] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A three-parameter coordinated adaptive control method for energy storage converter based on VSG, It is characterized in that The method comprises the following steps: S1: Add a virtual impedance in the virtual synchronous generator system, wherein the virtual impedance includes a virtual inductor and a virtual resistor; collect three-phase voltage and current data of the VSG output port and the grid connection point, and calculate the VSG output power difference, power change rate and angular frequency difference; S2: The power command is corrected by combining the power command and the grid angular frequency difference, the angular frequency oscillation curve is replaced by the power oscillation curve, and the oscillation process of the VSG output power is divided into 6 stages based on the power difference and the power change rate; S3: Calculate and adjust the moment of inertia, virtual damping and virtual inductance in 6 stages; S4: Detect the VSG output power difference and power change rate in 6 stages. When the power adjustment direction deviates from the corrected power command, readjust the virtual inductance based on the original control strategy to suppress the power deviation. Then detect whether the value of the virtual inductance deviates from the initial value. If it deviates from the initial value, compensate the virtual inductance with a small step to adjust the virtual inductance to the initial value. S5: Analyze the output impedance characteristics of the system through the transfer function of the output impedance, determine the value of the virtual resistance according to the variation range of the virtual impedance; and determine the selected virtual impedance according to the determined virtual inductance and virtual resistance.

2. According to claim 1, the three-parameter coordinated adaptive control method of the energy storage converter based on VSG, It is characterized in that The virtual synchronous generator system comprises a system main circuit and a control circuit connected to each other; wherein: The main circuit of the system includes a DC power supply, a three-phase inverter bridge arm and an LCL filter connected in sequence; The control circuit comprises a power outer loop, a voltage-current double closed loop and a PWM modulation part which are connected in sequence; a virtual impedance for power decoupling and power oscillation suppression is added to the voltage-current double closed loop.

3. According to claim 1, the three-parameter coordinated adaptive control method of the energy storage converter based on VSG, It is characterized in that The specific steps in S1 are: S11: Collect and record the three-phase voltage and current data of the VSG output port and the grid connection point at each moment during operation; S12: Perform clack transformation on the voltage and current output by the VSG, and calculate the active and reactive power output by the VSG in the α and β coordinate systems: Among them: U A , U B , U C is the three-phase voltage output by VSG; U α , U β P is the voltage of the VSG output three-phase voltage after clack transformation; e and Q e It is the active and reactive power output of VSG; S13: Calculate the angular frequency of the VSG output voltage and the grid common connection point voltage using a phase-locked loop.

4. According to claim 3, the three-parameter coordinated adaptive control method of the energy storage converter based on VSG, It is characterized in that The specific steps in S2 are: S21: Use the VSG output voltage angular frequency and the grid voltage angular frequency to correct the power command, where P set is the initial active power instruction of VSG; P set ' is the corrected active power instruction; D p is the active droop coefficient, i.e. the damping coefficient; ω o is the angular frequency of the VSG output voltage; ω g is the angular frequency of the grid-connected point voltage; P set '=P set +D p (oh o -oh g ) S21: Determine the demarcation point between the VSG power oscillation stages according to the corrected power command, power difference and power change rate, P u , P d are the upper and lower limits of the power reference threshold respectively; ΔP ω is the power increase of primary frequency modulation; ΔP s is the amplitude of low-frequency oscillation of output power of VSG in steady state; S22: The upper and lower limits of the power reference threshold and the power oscillation curve form at most four intersection points, namely, the dividing points of the oscillation cycle. According to the four dividing points and the extreme points of the oscillation cycle, one cycle of the power oscillation curve is divided into six stages: Where: P e is the electromagnetic power output by VSG; The VSG output power is divided into the following parts according to time in one oscillation cycle: Where: t 1 ~t 7 It is the time corresponding to each dividing point within an oscillation cycle.

5. According to claim 4, the three-parameter coordinated adaptive control method of the energy storage converter based on VSG, It is characterized in that The specific steps in S3 are: S31: The damping coefficient of VSG and the size of virtual rotation inertia will affect the damping of the system. According to the relationship between the system damping, the damping coefficient and the virtual rotation inertia, the virtual rotation inertia J is reduced when the VSG output power approaches the corrected power command, and the virtual rotation inertia J is increased when the VSG output power moves away from the corrected power command to adjust the virtual rotation inertia. Where: T m is the input torque of the prime mover, T e is the electromagnetic torque of VSG, ω is the angular frequency of VSG output voltage, ω n is the rated angular frequency, D p is the active droop coefficient, i.e. the damping coefficient, J 0 is the initial value of the virtual moment of inertia, J 1 is the original output value of the virtual moment of inertia; S32: Similarly, the virtual damping is adjusted according to the rule that the virtual damping D is reduced when the VSG output power approaches the corrected power command and the virtual damping D is increased when the VSG output power moves away from the corrected power command; Where: D p0 is the initial value of the damping coefficient, D p1 is the original output value of the virtual impedance; S33: The size of the virtual inductor will affect the amplitude and phase of the output voltage, but under power closed-loop control, the voltage amplitude and phase given by the voltage and current dual closed-loop will be compensated. The larger the virtual inductor is, the greater the impact on the output voltage and the greater the degree of system compensation. Therefore, the addition of the virtual inductor is equivalent to adding additional damping to the system. Similarly, the virtual inductor is adjusted according to the rule that the virtual inductance L is reduced when the VSG output power approaches the corrected power instruction and the virtual inductance L is increased when the VSG output power moves away from the corrected power instruction. Where: k 1 and k 2 are the adjustment coefficients of power change rate and power difference on virtual inductance respectively; L v0 is the initial value of the corrected virtual inductance, L v1 is the initial output value of the main part of the virtual inductor; when the system is in a transition state, L v1 Maintain the original value and avoid frequently adjusting the value of the virtual inductance near the transition state.

6. According to claim 5, the three-parameter coordinated adaptive control method of energy storage converter based on VSG, It is characterized in that The specific steps in S4 are: S41: Compensate the power command when the grid frequency is offset, and obtain the corrected power command as follows: P set '=P set +D p (oh n -oh g ) S42: When the grid frequency deviates, the amplitude of the power oscillation is often larger than when the power command changes, so the initial value of the virtual inductance is compensated: Where: L v0 is the initial value of the corrected virtual inductance. L base is the basic value of virtual impedance; ω g is the grid angular frequency; S42: The virtual inductor adopts an adaptive adjustment method. Its adjustment process will cause the amplitude and phase of the output voltage to change. Therefore, during the power adjustment process, the virtual inductor is fine-tuned in the opposite direction when the output power moves away from the target power according to the change trend of the output power, so as to reduce the fluctuation of the output power: Where: L v2(n) is the value of the virtual inductance fine-tuning part of the current sampling period; L v2(n-1) is the value of the virtual inductance fine-tuning part of the previous sampling cycle; ΔL 1 and ΔL 2 is the period adjustment value of the virtual inductor fine-tuning part; S43: The virtual circuit is divided into two parts, where L v1 is the main part of the virtual inductor, L v2(n) It is the fine-tuning part of the virtual inductor. At the same time, in order to ensure the smooth transition of the virtual inductor, its output is connected to a low-pass filter, that is: S44: To ensure power sharing in parallel with VSG, L v2(n-1) In steady state, the initial value is returned, and the virtual inductance is continuously adjusted to the initial value during the adjustment process. That is, when the virtual inductance deviates from the initial value, a small adjustment value is added or subtracted, where ΔL 3 The periodic adjustment value for returning the virtual inductance to its initial value: S45: In order for the fine-tuning part of the virtual impedance to work properly, the three periodic adjustment values ​​of the virtual impedance meet the following requirements: ΔL 1 >ΔL 3 >ΔL 2 。 7. The VSG-based three-parameter coordinated adaptive control method for energy storage converter according to claim 6, It is characterized in that The specific steps in S5 are: S51: In order to improve the response speed of the system, an output voltage feedforward link is added to the voltage and current double closed loop, and the voltage loop closed loop transfer function is as follows: Where: G I is the proportional controller of the current loop; L 1 and R 1 are the inductance and resistance of the filter on the far grid side respectively; C is the filter capacitor in the LCL filter; k p , k i are the proportional coefficient and integral coefficient of the voltage loop PI controller respectively; in VSG, the filter inductor L 1 The additional resistor R 1 Much smaller than the inductance L 1 , so R 1 Treat as 0; S52: The total impedance between VSG and the grid connection point after adding the virtual impedance is obtained from the voltage loop transfer function as follows: Z' o (s)=Z o (s)+G b2 (s)·(R v +sL v )+Z 2 Where: Z 2 is the line impedance, Z o is the output impedance of VSG; Z 2 is the line impedance between VSG and the grid connection point; S53: Based on the transfer function of the total output impedance, draw the Bode diagram of the total output impedance under different virtual resistances, and take the virtual resistance as the value of the output impedance that is closest to the pure inductance characteristic.

8. A three-parameter coordinated adaptive control system for energy storage converter based on VSG, It is characterized in that include: a memory for storing executable computer programs; The processor is used to implement the three-parameter coordinated adaptive control method of the energy storage converter based on VSG as described in any one of claims 1 to 7 when executing the executable computer program stored in the memory.

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