VSG parameter coordinated control method for energy storage capacity configuration optimization

Abstract

The application discloses a VSG parameter coordinated control method for energy storage capacity configuration optimization, and first establishes a VSG electromagnetic power small signal model, obtains a VSG electromagnetic power-mechanical power transfer function and a VSG mechanical angular frequency-mechanical power transfer function under inductive power grid conditions, and controls through an adaptive virtual inertia control function and a damping control function. The application has the advantages of being capable of inhibiting system frequency deviation, improving VSG system electromagnetic power response performance, and simultaneously optimizing system energy storage capacity configuration and the like.

Description

Technical Field

[0001] This invention relates to the field of power grid technology, and in particular to a VSG parameter coordination control method for optimizing energy storage capacity configuration. Background Technology

[0002] In traditional power systems, synchronous generators, with their large inertia and high damping characteristics, have proven beneficial for stable operation. However, the large-scale application of renewable energy in recent years has led to a gradual decrease in the proportion of total power generation from synchronous generators in traditional power grids. The high penetration rate of renewable energy has resulted in a reduction in the rotational inertia of traditional power systems. Simultaneously, the rapid response of power electronic devices and the intermittent and random characteristics of renewable energy have brought significant challenges to the operation and control of traditional power systems. Therefore, virtual synchronous generator (VSG) control technology applied to the power electronic device side has emerged.

[0003] VSG technology achieves operating characteristics similar to traditional synchronous generators by simulating the inertia and damping characteristics of synchronous generators. The difference lies in the fact that the inertial potential energy of a synchronous generator comes from its rotor mechanical energy, and its inertia coefficient is determined by the generator's physical parameters. In contrast, the inertial potential energy of a VSG comes from its energy storage unit or a few renewable energy generation devices with inertial potential energy. Furthermore, key control parameters (such as the inertia coefficient and damping coefficient) can be directly adjusted to improve system performance.

[0004] Currently, theoretical research on VSGs mainly revolves around single / multi-unit VSG collaborative control and stable operation, energy storage system optimization, low voltage ride-through, and parameter optimization. Existing literature primarily focuses on adaptive parameter control of underdamped VSG systems, with little research analyzing the dynamic performance and internal parameter relationships in overdamped VSG systems, and a lack of in-depth study on the impact of VSG system dynamic response on system energy storage capacity configuration. Particularly when the VSG system damping ratio is dynamically changing, there is still room for optimization in the dynamic response performance of active power and frequency. Existing control strategies improve dynamic response performance through adaptive adjustment of VSG parameters, but large-scale parameter adjustments in adaptive control require significant energy, thus increasing the demand on energy storage unit capacity configuration for VSG systems. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a VSG parameter coordination control method that can suppress system frequency offset, improve the electromagnetic power response performance of VSG system, and optimize system energy storage capacity configuration.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A VSG parameter coordination control method for optimizing energy storage capacity configuration, characterized by comprising the following steps:

[0008] S1. First, establish the small-signal model of VSG electromagnetic power as follows:

[0009]

[0010] In the formula, J and D represent virtual inertia and virtual damping coefficient, respectively; ω and ω0 represent the VSG mechanical angular frequency and the grid rated angular frequency, respectively; P m P e These represent the mechanical power and electromagnetic power of the VSG, respectively; δ is the power angle of the VSG; E is the excitation voltage; U g This refers to the grid voltage.

[0011] S2. Under inductive power grid conditions, the VSG electromagnetic power-mechanical power transfer function and the VSG mechanical angular frequency-mechanical power transfer function are obtained as follows:

[0012]

[0013] Wherein, the natural angular frequency ω n The expressions for the damping ratio ζ and the proportional coefficient K are as follows:

[0014]

[0015] S3. During control, the adaptive virtual inertia control function is:

[0016]

[0017] In the formula: k is the proportionality coefficient, Δω is the change in the system's angular frequency, and C is the threshold for the angular frequency offset; when the fluctuation of ω is less than C, the inertia of the VSG system is taken as the initial inertia J0; when the fluctuation of ω is greater than C, the rotational inertia of the VSG system is corrected according to the change and rate of change of ω.

[0018] The damping control function is:

[0019]

[0020] Where ζ satisfies the damping ratio control function:

[0021]

[0022] In the formula, ζ′ is the transient damping ratio at the beginning of the system response, which is taken as 0.4-0.7 times ζ0; ζ0 is the damping ratio of the system in the later stage of the response and the steady stage, which is greater than 1.

[0023] Furthermore, in step S3, the proportionality coefficient k satisfies the following formula:

[0024]

[0025] Furthermore, the feasible domain expression of the VSG system is:

[0026]

[0027] In the formula: C eq U represents the equivalent capacitance of the energy storage battery; CN This indicates the equivalent rated voltage of the energy storage battery under rated discharge conditions; C max J represents the maximum charge / discharge rate of the energy storage battery. eqmax This represents the maximum equivalent virtual inertia that the energy storage battery can provide.

[0028] In summary, the present invention has the advantages of suppressing system frequency shift, improving the electromagnetic power response performance of VSG system, and optimizing system energy storage capacity configuration. Attached Figure Description

[0029] Figure 1 This refers to the topology of VSG.

[0030] Figure 2 This is the VSG active power control loop.

[0031] Figure 3 This is the VSG reactive power control loop.

[0032] Figure 4 The relationship between the VSG root locus and parameters J and D.

[0033] Figures 5-7 The figures show the VSG electromagnetic power step response under overdamped, critically damped, and underdamped conditions, respectively.

[0034] Figure 8 This is the VSG power angle characteristic curve.

[0035] Figure 9 This is the rotor angular frequency oscillation curve.

[0036] Figure 10 and Figure 11 The figures show the frequency response curves of the overdamped and underdamped systems, respectively.

[0037] Figure 12 The change in work angle Δδ in region I under different damping ratios Ⅰ The ratio of the total change in work angle Δδ.

[0038] Figure 13 The control strategy block diagram for coordinated control of variable damping ratio parameters is shown.

[0039] Figure 14 To coordinate the control and fixed parameter control of the VSG electromagnetic power curve under the power step response.

[0040] Figure 15 To coordinate the control and fixed parameter control power step response of VSG mechanical angular frequency curves.

[0041] Figures 16-20 The figures show the active power response, frequency response, system damping ratio, virtual inertia, and virtual damping curves of the VSG system under coordinated control and fuzzy control power step response, respectively.

[0042] Figure 21 Energy storage output for different control strategies.

[0043] Figure 22 and Figure 23 The simulation results are shown for traditional VSG control and VSG control with variable damping ratio parameters, respectively. Detailed Implementation

[0044] The invention will now be described in further detail with reference to mathematical modeling analysis.

[0045] I. VSG Mathematical Model and Small Signal Analysis

[0046] VSG mathematical model: The typical topology of a VSG is as follows Figure 1 As shown in the figure, L f C f and L g These represent the inverter-side inductance, capacitor, and grid-side inductance, respectively, and the mechanical power P output by the renewable energy and energy storage unit. m Similar to the role of the prime mover M in a traditional power generation system, the electromagnetic power P output by the VSG-controlled inverter... e This is similar to the function of a synchronous generator (SG).

[0047] VSG technology incorporates the rotor motion equation and excitation voltage equation into the power stage of the inverter, simulating the inertia and damping effect of a synchronous generator to effectively improve the frequency stability of the AC microgrid. Its equivalent rotor motion equation is shown in equation (1):

[0048]

[0049] In equation (1): J and D represent virtual inertia and virtual damping coefficient, respectively; when the number of pole pairs is 1, the electrical angular frequency of the synchronous generator is equal to its mechanical frequency, ω and ω0 represent the mechanical angular frequency of the VSG and the rated angular frequency of the power grid, respectively, and δ is the power angle of the VSG; T m and T e P represents the prime mover torque and electromagnetic torque of the VSG;m P e These represent the mechanical power and electromagnetic power of the VSG, respectively.

[0050] Under normal circumstances, ω≈ω0 can be assumed, and thus the rotor motion equation and excitation voltage equation are as shown in equation (2):

[0051]

[0052] In equation (2): K U E represents the reactive voltage droop coefficient and the excitation voltage; U g U0 and Q0 represent the mains voltage and rated voltage, respectively; Q0 ​​and Q e These are the rated reactive power and the output reactive power, respectively. Specifically, Figure 2 and Figure 3 The active power control loop and reactive power control loop corresponding to equation (2) are shown in the figure.

[0053] Small signal analysis: Assuming the system operates under stable grid connection conditions and the line inductive reactance is much greater than the impedance (L>>R), the power expression of the VSG fed into the grid is as shown in equation (3).

[0054]

[0055] Considering that under grid-connected conditions, since the active power and frequency oscillation problem is mainly introduced by the active power control loop, the low-frequency power oscillation problem of VSG can usually be ignored by the reactive power control loop, that is, the influence of the reactive power control loop can be neglected in the subsequent small-signal analysis. Assuming ω0 is a constant, when the mechanical power of VSG changes abruptly, after small-signal linearization and Laplace transform of equations (1) and (3), the small-signal model of VSG electromagnetic power is as follows:

[0056]

[0057] Considering that δ is very small (cosδ≈1) under inductive grid conditions, and according to equation (4), the VSG electromagnetic power-mechanical power transfer function and the VSG mechanical angular frequency-mechanical power transfer function are obtained as follows:

[0058]

[0059] Wherein, the natural angular frequency ω n The damping ratio ζ and the proportional coefficient K are expressed as follows:

[0060]

[0061] When the inertia coefficient J = 0.2, 0.5, and 1, the trajectory of the system's characteristic roots changes as the damping coefficient D increases, as shown below. Figure 4As shown. Combining equation (6), it can be seen that the virtual inertia J affects the natural angular frequency of the VSG system, while the ratio of virtual inertia J to virtual damping D affects the damping ratio of the VSG system. The overshoot and oscillation mode of the system's step response mainly depend on ζ, while ω n This will primarily affect the response speed of the system's step response. Oscillations in the output response are common in the step response of traditional second-order systems, and the system's step response settling time t... s With system step response overshoot M p The contradictory issues also exist in VSG systems. To achieve better transient response performance than traditional VSGs, VSGs can dynamically adjust the damping ratio and natural oscillation frequency of the VSG system through inertia and damping, thereby optimizing the system's transient response.

[0062] II. Dynamic Response and Energy Storage Capacity Configuration Analysis

[0063] The damping and inertia coefficients of a VSG are closely related to the energy storage capacity of the system. Traditional adaptive VSG parameter control suppresses the oscillation of the system's electromagnetic power by dynamically adjusting the inertia and damping coefficients. However, large-scale adjustment of virtual inertia and virtual damping will increase the capacity requirements of the energy storage units, thus increasing the burden on the energy storage units. This paper analyzes the relationship between the dynamic response of the VSG system and the energy storage capacity under different damping ratios, and proposes a variable damping ratio coordinated control strategy to optimize the energy storage capacity and improve the dynamic response performance of the system's electromagnetic power.

[0064] Dynamic Response Analysis: The electromagnetic power and output frequency response of a traditional VSG system are affected by the system damping ratio and natural oscillation frequency. In underdamped, critically damped, and overdamped systems, the settling time serves as a primary reference indicator for the system's step response, mainly affecting the system's response speed. However, its precise expression and value are complex, and the following estimation expression is generally used in calculations:

[0065] ① Overdamped system (ζ>1)

[0066] In an overdamped VSG system, there is no overshoot. Its characteristic equation contains two real roots that are opposites of each other, λ1 and λ2. According to equation (5), the system's unit electromagnetic power step response and unit mechanical angular frequency step response can be obtained as follows:

[0067]

[0068] The two real roots of its characteristic equation are represented as follows:

[0069]

[0070] After inverse Laplace transforming the two equations in equation (7), we obtain their time-domain expressions as follows:

[0071]

[0072] In equation (9), both equations contain the same decay exponent term. and Furthermore, the two exponentially decaying terms decay at different rates, mainly influenced by the two time constant terms λ1 and λ2. According to equation (8), when ζ > 1, |λ1| >> |λ2|, meaning that the term containing λ1 in equation (9) decays much faster than the term containing λ2. Therefore, when the decay rate of one exponentially decaying term is much greater than that of the other, the two equations in equation (9) can be simplified into approximate expressions influenced only by one exponentially decaying term, as follows:

[0073]

[0074] Since the exponential decay terms in both equations (10) are the same, they have the same decay rate. When a 2% allowable error standard is taken, the settling time t of the overdamped VSG system... s1 It can be approximated as:

[0075]

[0076] Equation (11) indicates that under ideal conditions, when K and ω0 are considered constant in a fixed damping ratio system, the adjustment time of the overdamped system is positively correlated with the damping ratio and the inertia coefficient.

[0077] ② Critically damped system (ζ=1)

[0078] In a critically damped system, the system response is similar to that of an overdamped system. Since its characteristic equation has a pair of identical real roots, the system has two identical damping exponent terms: λ1 = λ2 = ω. n Equation (7) can then be written as:

[0079]

[0080] Similarly to the derivation process of the overdamped system above, the time-domain expressions for the unit electromagnetic power step response and the unit mechanical angular frequency step response of the critically damped VSG system can be obtained as follows:

[0081]

[0082] Its critical damped VSG system settling time t s2 It can be written as:

[0083]

[0084] ③ Underdamped system (0 < ζ < 1)

[0085] In an underdamped VSG system, the characteristic equation of its system response contains two complementary imaginary roots. Referring to the principles of automatic control, the time-domain expressions for the unit electromagnetic power step response and the unit mechanical angular frequency step response of the underdamped VSG system are as follows:

[0086]

[0087] Settling time t of the overdamped system s3 The overshoot σ% can be expressed as:

[0088]

[0089] When the allowable error band is 0.2%, according to equations (11), (14) and (16), the curve of the settling time changing with the system damping ratio initially shows a discontinuous and irregular change. The settling time is shortest when the damping ratio ζ>0.76, and then increases basically linearly. Combining equation (16), it can be seen that in an underdamped system, although the settling time is short and the response speed is fast, the system has an overshoot problem. Conversely, although there is no overshoot problem in an overdamped or critically damped system, the system settling time is relatively long and the response speed is slow. By comparing the settling time expressions of systems with different damping ratios, it can be seen that in the same VSG system, under the condition of the same natural oscillation frequency, the settling time of systems with different damping ratios basically follows the following inequality relationship:

[0090] t s1 >t s2 >t s3 (17)

[0091] Energy storage capacity configuration analysis: The VSG system consists of three main parts: renewable energy, energy storage units, and inverter units. When the output of the renewable energy power generation device is disturbed, i.e., P... m When disturbances occur, the energy storage unit is mainly responsible for absorbing or releasing energy to maintain the stability of the system, so it is necessary to analyze the capacity configuration of the energy storage unit.

[0092] Based on equations (9), (13), and (15), the electromagnetic power step response diagrams for overdamped, critically damped, and underdamped electromagnetic power can be obtained, as follows: Figures 5-7 As shown, when the system's electromagnetic power, or the output power P of the new energy device... m When a sudden change occurs, the VSG outputs mechanical power P. e Following P m During this transient process, the system's energy storage device needs to absorb or release energy. The shaded area represents the energy that the system's energy storage device needs to absorb or release. For example... Figure 5As shown, since the overdamped system's step response has no overshoot, the energy that the energy storage device needs to absorb during the entire step disturbance is:

[0093]

[0094] Equation (18) is also the minimum energy storage configuration capacity of the overdamped system.

[0095] Similar to overdamped systems, critically damped systems require their energy storage units to absorb the following energy:

[0096]

[0097] Due to the overshoot inherent in underdamped systems, the minimum required capacity of the energy storage unit is ΔP. e First arrival at ΔP m The energy absorbed at that moment, the time of which is described as t. q The energy absorbed is:

[0098]

[0099] In the same VSG system, assuming the natural oscillation frequency is the same, there is an inequality relationship between the minimum configuration capacity of energy storage units for systems with different damping ratios:

[0100] E1 > E2 > E3 (21)

[0101] From the above formula, we can see that: overdamped systems require relatively large energy storage capacity configuration; underdamped systems require relatively small energy storage capacity configuration, but they have overshoot, which will cause the battery to be repeatedly charged and discharged, damaging the battery life; the energy storage capacity configuration requirement of critically damped systems tends to be between the two.

[0102] Based on the above analysis, the key conclusions are as follows: ① Overdamped and critically damped VSG systems have longer adjustment times, slower response speeds, no overshoot, and larger energy storage capacity requirements; ② Underdamped VSG systems have shorter adjustment times, faster response speeds, overshoot, and smaller energy storage capacity requirements.

[0103] Combination Figures 5-7 Intuitive analysis reveals that to optimize system energy storage capacity configuration and reduce the energy storage capacity required for system power response (meaning the shaded area in the diagram needs to be as small as possible while ensuring system stability), the electromagnetic power response curve of the VSG system should rapidly approach the steady-state mechanical power value in the initial stage of the step response to minimize the output of the energy storage unit. Conversely, in the later stage of the system's active power response, active power overshoot should be suppressed to prevent repeated charging and discharging of the energy storage system.

[0104] III. Coordinated Control Method for Variable Damping Ratio Parameter

[0105] Combining the advantages of both overdamped and underdamped systems, this embodiment proposes a variable damping ratio parameter coordinated control strategy. By adjusting the system damping ratio reasonably throughout the entire step response process, and then coordinating the adaptive changes of virtual inertia and virtual damping according to the damping ratio coefficient, the system frequency shift is suppressed, the electromagnetic power response performance of the VSG system is improved, and the system energy storage configuration is optimized.

[0106] Adaptive parameter adjustable range For grid-connected inverters based on VSG control, the bandwidth of the voltage and current dual closed-loop is wider than that of the VSG power loop, so the stability of the VSG power loop is generally considered. However, the stability and output response of the VSG power loop are mainly affected by the damping ratio and the natural oscillation frequency. Adjusting the inertia and damping is actually achieving better step response performance by changing the system's damping ratio and natural oscillation frequency. The following are the adjustable ranges of parameters considered for stable operation of the VSG system.

[0107] According to the Routh stability criterion, the necessary and sufficient conditions for the active closed-loop stability of the VSG are: J > 0, D > 0. That is, the system's virtual inertia and virtual damping must be positive, and the system's gain margin must be greater than zero. Simultaneously, the system needs to reserve a phase margin to ensure stable operation, and the system's characteristic root should be a certain distance from the imaginary axis to ensure a large attenuation factor and rapid decay of transient components. Finally, considering that the energy for suppressing mechanical angular frequency shift in the VSG system comes from renewable energy generators or energy storage devices, the inertia provided by the renewable energy units or energy storage units needs to be considered when adjusting the VSG's virtual inertia and virtual damping. The specific feasible region expression for this is as follows:

[0108]

[0109] Equation (22): C eq U represents the equivalent capacitance of the energy storage battery; CN This indicates the equivalent rated voltage of the energy storage battery under rated discharge conditions; C max J represents the maximum charge / discharge rate of the energy storage battery. eqmax This represents the maximum equivalent virtual inertia that the energy storage battery can provide.

[0110] Variable damping ratio parameter coordinated control strategy frequency and power angle description From equation (3), the power angle characteristic curve of the VSG system is as follows: Figure 8 and Figure 9 As shown in the figure, ω is the mechanical angular frequency of the VSG system, and ω0 is the rated angular frequency of the power grid. When the mechanical power P of the VSG system... m When a disturbance or sudden change occurs, ω oscillates and loses synchronization with the grid's rated angular frequency ω0, with a mechanical angular frequency offset of Δω = ω - ω0. If the system is in a sufficiently stable state, ω can regain synchronization with the grid's rated angular frequency after the oscillation. Figure 9In the process, as ω changes from point a to point b, in region I, Δω > 0 and dω / dt > 0. The mechanical angular frequency offset of the VSG system is greatest at point b. Subsequently, it changes from point b to point c, during region II, Δω > 0 and dω / dt < 0. At point c, due to t... a to t c During this period, the cumulative mechanical angular frequency offset causes the VSG system's power angle δ to change the most, at which point the VSG system's electromagnetic power P... e It reaches its maximum value. Then ω changes to below ω0, repeating a similar process until equilibrium is reached, which is the change in mechanical power ΔP. m When the total power angle change Δδ of the system is determined, the total power angle change Δδ of the system is also determined.

[0111] From the above process description, it can be concluded that the mechanical angular frequency of the VSG oscillates around the rated angular frequency of the power grid, thereby causing oscillations in the system's power angle, resulting in oscillations and overshoot of the system's active power. From equations (9) and (15), it can be seen that the frequency response curve of the underdamped VSG system changes as a decaying sin function, while the frequency response curve of the overdamped VSG system first deviates from the rated angular frequency and then changes as an approximately exponential function.

[0112] Figure 10 and Figure 11 The frequency response curves of overdamped and underdamped systems are shown, and the change in work angle Δδ of the underdamped system in region I is compared. Ⅰud Compared to the overdamped system, Δδ Ⅰod The change in power angle is relatively large. As can be seen from equation (3), the system's electromagnetic power changes rapidly, and the system's electromagnetic power quickly approaches the new power equilibrium point. In the middle and late stages of the response, the underdamped system experiences overshoot and oscillation of electromagnetic power due to the oscillation of the angular frequency at the rated angular frequency point. In contrast, the overdamped system has a relatively slow response speed in the middle and late stages of the response, but no overshoot.

[0113] Figure 12 The change in work angle Δδ in region I under different damping ratios Ⅰ The ratio of the total power angle change Δδ to the electromagnetic power response of the VSG system indirectly represents the speed of the electromagnetic power response. As shown in the figure, the ratio gradually decreases as the system damping ratio increases. If the VSG system is made underdamped in region I, the system's mechanical angular frequency varies as a sine function, and the system's electromagnetic power P... eThe system rapidly approaches a new power equilibrium point. In region II, the system is placed in an overdamped state, causing its mechanical angular frequency to approach the rated angular frequency in a quasi-exponential manner. This suppresses excessively rapid changes in the system's mechanical angular frequency, allowing the system's electromagnetic power to reach a new equilibrium point within the region I to II, thereby reducing or even eliminating system overshoot. The process of the system's mechanical angular frequency change using the above control strategy is similar to the frequency step response curve of an overdamped system, but with a faster response speed, satisfying the aforementioned requirements of fast response and no overshoot.

[0114] Coordinated control strategy for variable damping ratio parameters Based on the above, the variable damping ratio parameter coordinated adaptive control strategy proposed in this embodiment is as follows:

[0115] First, the damping ratio of the system needs to change according to the above process. Therefore, the damping ratio control function needs to be described as follows:

[0116]

[0117] In equation (23), ζ′ is the transient damping ratio at the beginning of the system response, which makes the system respond faster in the early stage of the step response. It is generally taken as 0.4-0.7 times ζ0. ζ0 is the damping ratio of the system in the later stage of the response and the steady stage. It is generally taken as greater than 1. The overdamping ratio suppresses the overshoot of the system in the later stage of the step response.

[0118] Based on the mainstream adaptive virtual inertial control concept, the inertia is increased when the angular frequency deviates from the rated angular frequency to suppress excessive angular frequency deviation. The adaptive virtual inertia control function is as follows:

[0119]

[0120] In equation (24): k is the proportionality coefficient, Δω is the change in the system angular frequency, and C is the threshold of the angular frequency offset.

[0121] When the fluctuation of ω is less than C, the inertia of the VSG system remains at the initial inertia J0. When the fluctuation of ω is greater than C, the rotational inertia of the VSG system is corrected according to the amount and rate of change of ω. Clearly, using the threshold C to determine whether ω exceeds the specified range reduces the variation in J caused by minor errors during the detection process, thus ensuring system stability. Furthermore, while increasing J can suppress excessive angular frequency shifts, maintaining a relatively stable damping ratio requires simultaneously increasing D, which increases the burden on the energy storage unit. Therefore, to ensure reliability, J cannot be too large, and the value of k needs to be designed based on the maximum value of J, as follows:

[0122]

[0123] The system's virtual damping coefficient D changes according to the system's damping ratio ζ and inertia coefficient J, causing the system's damping ratio to change according to the pattern shown in equation (23). The damping control function for this is as follows:

[0124]

[0125] The control strategy block diagram for coordinated control of variable damping ratio parameters is as follows: Figure 13 As shown, the power angle control module transmits the rated angular frequency and mechanical angular frequency signals to the parameter adaptive module, which processes them and then transmits them back to the power angle control module to form a closed loop.

[0126] IV. Simulation Verification

[0127] To verify the correctness and effectiveness of the theory and control strategy described in this embodiment, a system was built on the Matlab / Simulink platform as follows: Figure 1 The parameters of the grid-connected VSG model shown are shown in Table 1.

[0128] Table 1 Grid-connected VSG parameters

[0129]

[0130]

[0131] Simulation verification of sudden change in mechanical power: The system initially carries a rated load of 100kW. At 0.5s, the mechanical power of the VSG system jumps from 100kW to 200kW. A comparative analysis was conducted using fixed-parameter control, parameter-coordinated control, and fuzzy adaptive control. To minimize the impact of different system damping ratios on the control performance comparison, the damping ratio of the underdamped system was standardized at 0.707, and the damping ratio of the overdamped system was standardized at 1.3. Specific parameters are as follows:

[0132] 1) Underdamped fixed parameter control: J = 2, D = 91, ζ = 0.707.

[0133] 2) Overdamped fixed parameter control: J = 2, D = 168, ζ = 1.3.

[0134] 3) Underdamped fuzzy adaptive control: J0 = 2, D0 = 91, ζ = 0.707.

[0135] 4) Overdamped fuzzy adaptive control: J0 = 2, D0 = 168, ζ = 1.3.

[0136] 5) Parameter coordination control: J0 = 2, ζ′ = 0.707, ζ0 = 1.3.

[0137] Figure 14 and Figure 15The waveforms of active power and frequency output by the VSG system are shown when the system employs fixed parameter control and parameter coordination control. Figure 14 and Figure 15 In the case of a VSG system employing a variable damping ratio parameter coordinated control strategy, the system is underdamped in the initial stage of active power response, resulting in a relatively short settling time and faster active power response compared to an overdamped system. In the later stage of active power response, the system becomes overdamped. Due to the greater damping, active power oscillations are suppressed, reducing active power overshoot compared to an underdamped system. The maximum frequency deviation of the system falls between that of an underdamped and overdamped system, but the system frequency recovery is relatively faster. Overall, the variable damping ratio parameter coordinated control combines the advantages of overdamped and underdamped fixed parameter control, resulting in a shorter settling time and lower overshoot.

[0138] Since fuzzy adaptive control works well in traditional adaptive control strategies, the system is compared with fuzzy adaptive control using variable damping ratio parameter coordinated control. Figures 16-20 The graphs show the active power response, frequency response, system damping ratio, virtual inertia, and virtual damping curves of the VSG system. Compared to traditional fuzzy adaptive control, the variable damping ratio parameter coordinated control exhibits similar response speeds in the early and mid-stages of the active power step response. However, in the later stages of the response, the system is in an overdamped state, suppressing active power overshoot. The system overshoot is significantly smaller, and the settling time is also slightly shorter. Overall, traditional fuzzy adaptive control methods require frequent changes to the system's virtual inertia and virtual damping based on the system state, resulting in high computational complexity, poor stability, and unstable system damping ratio. The parameter coordinated control strategy proposed in this paper exhibits relatively stable virtual inertia, virtual damping, and damping ratio during the power step response, with lower computational complexity.

[0139] Optimization of energy storage capacity configuration verification: To verify the optimization effect of the variable damping ratio parameter coordinated control strategy described in this paper on energy storage capacity configuration, fixed parameter control and fuzzy adaptive control were used for comparative analysis, and the simulation parameters were consistent with those described above.

[0140] like Figure 21 It can be seen that the energy storage capacity required by the underdamped system oscillates due to the oscillation of the system's output active power, eventually stabilizing. Overall, the energy storage capacity required by an underdamped system is smaller than that required by an overdamped system, and the energy storage capacity requirement is generally higher for systems using fuzzy adaptive control compared to those using fixed parameter control. However, when the system uses parameter coordinated control and is also in an overdamped state, the required energy storage capacity decreases significantly compared to the previous two control methods, but increases compared to the underdamped system shown in the figure.

[0141] The minimum energy storage configuration required for each control method is shown in Table 2:

[0142] Table 2 Minimum Energy Storage Configuration under Different Control Strategies

[0143]

[0144] Hardware-in-the-loop semi-physical simulation verification: To further verify the effectiveness and feasibility of the proposed control strategy, hardware-in-loop (HIL) semi-physical simulation was performed on the RT-LAB OP5600 platform. The proposed VSG model was programmed from the Simulink environment into the RT-LAB system, thus replacing the system's hardware components. The control strategy of the VSG model was implemented by a DSP. The voltage and current signals generated by the RT-LAB were transmitted to the DSP, which then calculated and generated a PWM signal, feeding it back to the RT-LAB to form a closed loop. Compared to Simulink simulation, HIL simulation more closely resembles the actual circuit environment and can verify the feasibility and effectiveness of the control strategy.

[0145] If the parameters used in the HIL device are consistent with those used in the simulation, then comparing the simulation results with the HIL simulation results is feasible. As follows: Figure 22 and Figure 23 As shown, the HIL results of the conventionally controlled VSG and the VSG with coordinated control of the variable damping ratio parameters agree well with the simulation results. During the experiment, the coordinated control strategy effectively optimized the dynamic response of the VSG. The results verify the effectiveness and feasibility of the proposed control strategy.

[0146] Conclusion: This embodiment takes a traditional VSG as the research object, analyzes the dynamic performance and energy storage capacity configuration of systems with different damping ratios, and proposes a variable damping ratio parameter coordinated control strategy to optimize the system's energy storage capacity configuration and improve the system's dynamic response, combining the advantages of underdamped and overdamped systems. The effectiveness of the proposed method is verified through simulation. The main conclusions are summarized in the following three points:

[0147] 1) The proposed parameter coordination control strategy is actually a kind of overdamped system. It is an overdamped system in a steady state, and when the system is disturbed, it exhibits adaptive changes between underdamped and overdamped states.

[0148] 2) The proposed parameter coordination control strategy reduces the minimum energy storage configuration by about 17% compared to a system with the same steady-state damping ratio ζ0, and increases the minimum energy storage configuration by about 8.75% compared to a system with the same transient damping ratio ζ'.

[0149] 3) The proposed parameter coordination control strategy has a small computational load, and can suppress the spike in the instantaneous change of the moment of inertia parameter during disturbances, and the parameter curve changes smoothly.

[0150] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A VSG parameter coordination control method for optimizing energy storage capacity configuration, characterized in that, Includes the following steps: S1. First, establish the small-signal model of VSG electromagnetic power as follows: In the formula, J and D represent virtual inertia and virtual damping coefficient, respectively; , These represent the VSG mechanical angular frequency and the grid rated angular frequency, respectively. , These represent the mechanical power and electromagnetic power of the VSG, respectively. The power angle of the VSG; E is the excitation voltage; U g This refers to the grid voltage. S2. Under inductive power grid conditions, the VSG electromagnetic power-mechanical power transfer function and the VSG mechanical angular frequency-mechanical power transfer function are obtained as follows: Among them, natural angular frequency Damping ratio and proportionality coefficient The expression is as follows: ； S3. During control, the adaptive virtual inertia control function is: Where: k is the proportionality coefficient, Let ω be the change in system angular frequency, and C be the threshold for angular frequency offset. When the fluctuation of ω is less than C, the inertia of the VSG system is taken as the initial inertia J0. When the fluctuation of ω is greater than C, the rotational inertia of the VSG system is corrected according to the change and rate of change of ω. The damping control function is: in Satisfy the damping ratio control function: In the formula The transient damping ratio at the start of the system response is taken as 0.4-0.7 times. ; This is the damping ratio of the system in the later stage of response and the steady stage, and its value is greater than 1; In step S3, the proportionality coefficient k satisfies the following formula: The feasible domain expression of the VSG system is: In the formula: C eq U represents the equivalent capacitance of the energy storage battery; CN This indicates the equivalent rated voltage of the energy storage battery under rated discharge conditions; C max This represents the maximum charge / discharge rate of the energy storage battery; This represents the maximum equivalent virtual inertia that the energy storage battery can provide.

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