Damping control method suitable for constructing network type energy storage under new energy output fluctuation

Abstract

The invention provides a damping control method suitable for constructing network type energy storage under new energy output fluctuation, and belongs to the technical field of power electronic converter control, the control method comprises a power grid voltage sampling circuit, an inductive current sampling circuit, a bus voltage sampling circuit and a digital control unit; the digital control unit comprises an abc / dq converter, a dq / abc converter, a new energy equipment current PI regulator, a new energy bus voltage PI regulator, a new energy equipment PWM controller, a new energy power calculator, an energy storage virtual synchronous controller, an energy storage current PI regulator, an energy storage voltage PI regulator, an energy storage voltage feedforward controller, an energy storage PWM controller and an energy storage virtual damping calculator. And an energy storage power calculator, a subtracter, a multiplier and a divider. The control method fully considers the influence of the new energy output fluctuation characteristics on the parallel connection network construction type energy storage, and can alleviate the problem of insufficient damping caused by the new energy output fluctuation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power electronic converter control, and particularly relates to a damping control method suitable for grid-forming energy storage under new energy output fluctuation. BACKGROUND

[0002] With the increasing penetration of renewable energy, large-scale new energy generation systems are connected to weak power grids. In this scenario, subsynchronous oscillation is easily induced between the new energy grid-connected converter and the weak grid impedance, threatening system operation safety. To address this problem, existing research mostly uses grid-forming energy storage connected in parallel at the grid-connected point to suppress subsynchronous oscillation. However, the integration of grid-forming energy storage into the new energy grid-connected converter introduces new phase angle synchronous coupling, which has complex dynamic interaction with the inherent grid-following control characteristics of new energy equipment. Although the integration of energy storage can enhance the grid strength at the grid-connected point and provide auxiliary damping for subsynchronous oscillation of the new energy grid-connected converter, few documents study the influence of grid-following new energy on grid-forming energy storage, especially when the new energy output has obvious fluctuation characteristics. When the steady-state operating point of new energy changes, it will interact with the grid-forming energy storage through the loop, affecting the damping characteristics of the grid-forming energy storage, and causing low-frequency oscillation problems of the grid-forming energy storage converter. SUMMARY

[0003] To overcome the defects of the prior art, the present application provides a damping control method suitable for grid-forming energy storage under new energy output fluctuation, which can adaptively optimize the virtual damping parameters of the grid-forming energy storage according to the output state of the new energy, suppress the power angle oscillation of the grid-forming energy storage when the new energy output decreases, and improve the operation stability of the grid-following new energy and grid-forming energy storage parallel system.

[0004] The present application provides a damping control method suitable for grid-forming energy storage under new energy output fluctuation, which comprises: S10: by establishing the filter dynamic equation and the inner loop control loop dynamic equation of the grid-following new energy converter and the grid-forming energy storage converter, an inner loop admittance model of the grid-following new energy converter and the grid-forming energy storage converter is constructed; S20: based on the established inner loop admittance model, when a small disturbance occurs in the grid voltage phase, an electrical equation of the output current and the grid voltage of the grid-following converter and the grid-forming converter in their respective synchronous coordinate systems is constructed, and a transformation equation of each electrical quantity between the grid-following coordinate system and the grid-forming coordinate system is established; S30: based on the transformation equation of each electrical quantity between the grid-following coordinate system and the grid-forming coordinate system, and combined with the phase disturbance generated by the grid-following and grid-forming synchronous coordinate systems when a small disturbance occurs in the grid voltage phase, an expression for transforming the grid voltage from the global coordinate system to the grid-following coordinate system and the grid-forming coordinate system is constructed; S40: Based on the expressions of the grid-connected point voltage in the grid-following coordinate system and the grid-forming coordinate system, combined with the coordinate transformation equations of each electrical quantity, a small signal perturbation model of the grid-following new energy output voltage and the grid-forming energy output current in their respective synchronous coordinate systems is constructed when the grid voltage phase is disturbed; S50: Based on the established small signal perturbation model, the phase angle interaction relationship between the grid voltage phase disturbance and the grid-following and grid-forming coordinate system phase disturbance is established, and a grid voltage phase disturbance-grid-forming energy phase disturbance closed-loop transfer function for judging the stability of the energy storage equipment, i.e., the synchronous dominant loop of the grid-forming energy converter, is constructed; S60: Based on the constructed synchronous dominant loop, a stability criterion of the grid-forming energy storage equipment is established, a target function and parameter constraint condition of the grid-forming energy virtual damping adjustment near the new energy storage and grid connection system subsynchronous oscillation frequency are constructed, and an optimization equation is established to calculate the corresponding virtual damping to adjust the damping coefficient of the grid-forming energy virtual synchronous control.

[0005] Preferably, the establishment of the inner loop admittance model of the grid-following new energy converter and the grid-forming energy converter through the establishment of the dynamic equations of the filter and the inner loop control loop of the grid-following new energy converter and the grid-forming energy converter, comprises: The dynamic equations of the LC filter and the current control loop of the grid-following new energy converter are established, and the complex vector form of the grid-following new energy converter inner loop admittance model is constructed according to the established dynamic equations; The dynamic equations of the LC filter, the current control loop, the voltage control loop and the virtual impedance control of the grid-forming energy converter are established, and the complex vector form of the grid-forming energy converter inner loop admittance model is constructed according to the established dynamic equations.

[0006] Preferably, based on the established inner loop admittance model, when the grid voltage phase is disturbed, the electrical equation of the output current of the grid-following converter and the grid-forming converter in their respective synchronous coordinate systems and the grid-connected point voltage is constructed, and the transformation equation of each electrical quantity between the grid-following coordinate system and the grid-forming coordinate system is established, comprising: Based on the fact that the grid-following converter and the grid-forming converter adopt different synchronous controls to track the grid phase, the grid-following new energy equipment and the grid-forming energy equipment need to realize vector control in their respective synchronous coordinate systems. Let the local synchronous coordinate system of the grid-following new energy be NE, the local synchronous coordinate system of the grid-forming energy be ES, and introduce a global coordinate system C, which rotates at a constant rated angular velocity during the small disturbance of the grid; Based on the above coordinate system setting, when a small disturbance occurs in the phase of the grid voltage, the electrical equations of the output currents of the grid-connected converter and the grid-forming converter and the grid point voltage in the grid-following coordinate system NE and the grid-forming coordinate system ES are constructed, which include the relationship between the output current of the new energy and the grid point voltage in the grid-following coordinate system NE, and the relationship between the output current of the energy storage and the grid point voltage in the grid-forming coordinate system ES. The transformation equations of each electrical quantity between the grid-following coordinate system NE and the grid-forming coordinate system ES are constructed, including the transformation equations of the grid point voltage between the grid-following coordinate system NE and the grid-forming coordinate system ES, and the transformation equations of the output currents of the grid-connected converter and the grid-forming converter between the grid-following coordinate system NE and the grid-forming coordinate system ES.

[0007] Preferably, based on the transformation equations of each electrical quantity between the grid-following coordinate system and the grid-forming coordinate system, and combined with the phase disturbance caused by the synchronous coordinate system of the grid-following and the grid-forming when a small disturbance occurs in the phase of the grid voltage, the expressions for transforming the grid point voltage from the global coordinate system to the grid-following coordinate system and the grid-forming coordinate system are constructed, including: When a small disturbance occurs in the phase of the grid voltage, the small-signal expressions of the phase disturbance of the grid-following new energy synchronous coordinate system and the phase disturbance of the grid-forming energy storage synchronous coordinate system are respectively constructed, and the grid-side circuit equation in the global coordinate system is established; According to the above established transformation equations of the grid point voltage, the output currents of the grid-connected converter and the grid-forming converter between different coordinate systems, when a small disturbance occurs in the phase of the grid voltage, the expressions for transforming the grid point voltage from the global coordinate system C to the grid-following coordinate system NE and the grid-forming coordinate system ES are constructed.

[0008] Preferably, based on the expressions of the grid point voltage in the grid-following coordinate system and the grid-forming coordinate system, and combined with the coordinate transformation equations of each electrical quantity, the small-signal disturbance models of the output voltage of the grid-following new energy and the output current of the grid-forming energy storage in their respective synchronous coordinate systems when the phase of the grid voltage is disturbed are constructed, including: According to the above constructed expressions of the grid point voltage in the grid-following coordinate system NE and the grid-forming coordinate system ES, combined with the transformation equations of the output currents of each converter and the grid point voltage between different coordinate systems, the expressions of the grid point voltage in the grid-following coordinate system NE and the grid-forming coordinate system ES about the phase disturbance are respectively constructed; Based on the relationship between the grid point voltage and the output voltage of the new energy and the output current of the energy storage, the small-signal disturbance model of the output voltage of the new energy in the grid-following coordinate system NE and the small-signal disturbance model of the output current of the energy storage in the grid-forming coordinate system ES are established; The synchronous phase of the two converters affects the output voltage of the grid-connected new energy and the output current of the grid-constructing energy, and the change of the output voltage of the grid-connected new energy affects the grid-connected synchronous phase through the phase-locked loop, and the change of the output current of the grid-constructing energy affects the grid-constructing synchronous phase through the power synchronization loop, thereby forming a closed loop.

[0009] Preferably, based on the established small signal disturbance model, the phase angle interaction formula of the grid voltage phase disturbance and the grid-constructing coordinate system phase disturbance is established, and a grid voltage phase disturbance-grid-constructing energy phase disturbance closed loop transfer function for judging the stability of the energy equipment is constructed, that is, the synchronous dominant loop of the grid-constructing energy converter, including: Based on the established small signal disturbance model of the output voltage of the grid-connected new energy, combined with the small signal expression of the grid-connected coordinate system phase disturbance, the phase angle interaction expression of the grid voltage phase disturbance and the grid-connected coordinate system phase disturbance is constructed; Based on the established small signal disturbance model of the output current of the grid-constructing energy, combined with the small signal expression of the grid-constructing coordinate system phase disturbance, the phase angle interaction expression of the grid voltage phase disturbance and the grid-constructing coordinate system phase disturbance is constructed; According to the established phase angle interaction expression, a grid voltage phase disturbance-grid-constructing energy phase disturbance closed loop transfer function for judging the stability of the energy converter is constructed, that is, the synchronous dominant loop of the grid-constructing energy converter. According to the established synchronous dominant loop, the open loop transfer function of the grid-constructing energy converter can be obtained.

[0010] The open loop transfer function integrates the electrical relationship of the interconnected system line, the grid-constructing inner loop control loop and the dynamic characteristics of the grid-connected type new energy phase-locked loop, and contains information such as the stable operating point of the new energy and the energy, so it is affected by the output power of the new energy. The other part of the open loop transfer function contains the dynamic characteristics of the grid-constructing type energy synchronization link and the controllable damping parameters of the energy. Therefore, the constructed synchronous dominant loop of the grid-constructing energy converter contains the new energy output power variable and the controllable damping parameters of the energy, which can be used to analyze the influence of the new energy output on the stability of the grid-constructing energy equipment.

[0011] Preferably, based on the constructed synchronous dominant loop, the stability criterion of the grid-constructing energy equipment is established, the target function and parameter constraint condition of the grid-constructing type energy virtual damping adjustment near the subsynchronous oscillation frequency of the new energy energy interconnected system are constructed, and the optimization equation is established to calculate the corresponding virtual damping to adjust the damping coefficient of the virtual synchronous control of the grid-constructing type energy, including: Based on the synchronous dominant loop, the stability criterion of the system is established according to the two parts contained in the open loop transfer function of the grid-constructing energy converter. The stability criterion divides the system dynamics into two parts, so it can better and more intuitively analyze the interaction of the power synchronization loop dynamics and the grid-connected new energy equipment dynamics and reveal the corresponding instability mechanism.

[0012] Based on the established stability criteria for grid-type energy storage equipment, an objective function and parameter constraints for virtual damping adjustment of the new energy grid-connected system and parallel grid-type energy storage near the subsynchronous oscillation frequency of new energy storage are constructed, and an optimization equation is established. According to the optimization equation, the corresponding virtual damping amount is calculated to adjust the damping coefficient of the virtual synchronization control link of grid-type energy storage, thereby suppressing the risk of subsynchronous oscillation under the fluctuation of new energy output.

[0013] Compared with existing technologies, the beneficial effects are: This invention fully considers the impact of renewable energy output fluctuations on the power angle oscillation damping characteristics of grid-connected energy storage, improving the operational stability of grid-connected energy storage converters under renewable energy output fluctuations. Simulation and experimental verification show that, under renewable energy output fluctuations, the damping control method designed in this invention for grid-connected energy storage adaptively optimizes the virtual damping parameters of the grid-connected energy storage based on the renewable energy output status, suppressing power angle oscillations when renewable energy output decreases, and improving the operational stability of the parallel system of renewable energy and grid-connected energy storage. Therefore, the damping control method for parallel grid-connected energy storage under renewable energy output fluctuations designed in this invention has significant application value in power systems with high proportions of renewable energy integration and surging energy storage demand. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart of a damping control method for grid-type energy storage applicable to fluctuations in new energy output, according to the present invention. Figure 2 This is a control structure diagram of the method proposed in this invention; Figure 3 The frequency waveform diagram of the grid-type energy storage system when the output of the grid-type new energy source decreases, which is the damping control method of the present invention. Detailed Implementation

[0016] To make the objectives and technical solutions of the embodiments of this application clearer, the specific implementation methods of a damping control method for grid-type energy storage applicable to fluctuations in new energy output will be described in detail below with reference to the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the described embodiments of this application without creative effort are within the scope of protection of this application.

[0017] like Figure 1 As shown, the damping control method of the present invention for grid-type energy storage under the fluctuation of new energy output includes the following steps: S10: By establishing the filter dynamic equations and inner loop control loop dynamic equations for grid-connected new energy converters and grid-connected energy storage converters respectively, an inner loop admittance model for grid-connected new energy converters and grid-connected energy storage converters is constructed. S20: Based on the established inner loop admittance model, when the grid voltage phase is slightly disturbed, the electrical equations of the output current and grid connection point voltage of the grid-connected converter and the grid-connected converter in their respective synchronous coordinate systems are constructed, and the transformation equations of each electrical quantity between the grid-connected coordinate system and the grid-connected coordinate system are established. S30: Based on the transformation equations of each electrical quantity between the grid-connected coordinate system and the grid-connected coordinate system, and combined with the phase disturbance generated by the synchronous coordinate system of the grid-connected and grid-connected systems when the grid voltage phase undergoes a small disturbance, an expression is constructed to transform the grid connection point voltage from the global coordinate system to the grid-connected coordinate system and the grid-connected coordinate system respectively. S40: Based on the expression of the grid connection point voltage in the grid-connected coordinate system and the grid-connected coordinate system, and combined with the coordinate transformation equations of various electrical quantities, construct small-signal disturbance models of the grid-connected new energy output voltage and the grid-connected energy storage output current in their respective synchronous coordinate systems when the grid voltage phase disturbance occurs. S50: Based on the established small-signal disturbance model, establish the phase angle interaction relationship between the grid voltage phase disturbance and the phase disturbance of the grid-connected and grid-connected coordinate systems, respectively, and construct the grid voltage phase disturbance-grid-connected energy storage phase disturbance closed-loop transfer function for judging the stability of energy storage equipment, that is, the synchronous dominant loop of the grid-connected energy storage converter. S60: Based on the constructed synchronous dominant loop, establish the stability criteria for grid-connected energy storage equipment, construct the objective function and parameter constraints for virtual damping adjustment of grid-connected energy storage near the subsynchronous oscillation frequency of the new energy storage parallel system, establish the optimization equation, and calculate the corresponding virtual damping to adjust the damping coefficient of the virtual synchronous control of grid-connected energy storage.

[0018] In step S10, please refer to Figure 1Step S10 involves establishing the filter dynamic equations and inner-loop control loop dynamic equations for both the grid-connected renewable energy converter and the grid-connected energy storage converter, thereby constructing the inner-loop admittance model for both types of converters. Specifically, this includes: according to Figure 2 The control method shown is used to construct a controller. dq coordinate system LC The dynamic equation of the filter is expressed by the following formula:

[0019] in, The converter's machine-side voltage vector. v Cdq+ For the output voltage vector, i Ldq+ The inductor current vector. i dq+ For the output current vector, L f For filtering inductors, C f This is a filter capacitor.

[0020] according to Figure 2 The control structure of the control circuit shown is used to construct the dynamic equation of the current control loop of the grid-connected new energy converter, which is expressed by the following formula:

[0021] in, i dqref+ As the reference current vector, L f_NE For the filter inductor of the grid-connected new energy converter, PI C ( s ) is the transfer function of the current loop PI controller. k VF This is the voltage feedforward coefficient.

[0022] According to the grid-connected new energy converter LC The dynamic equations of the filter and current control loop are used to construct a complex vector form inner-loop admittance model for the grid-connected new energy converter, expressed by the following formula:

[0023] in, Y IV_NE+ and Y IV_NE- These are the positive and negative sequence admittances of the inner loop of the grid-connected new energy converter, respectively. C f_NE For the filter capacitor of the grid-connected new energy converter.

[0024] according to Figure 2The control structure of the control circuit shown is used to construct the dynamic equations of the current control loop and voltage control loop of the grid-type energy storage converter, which are expressed by the following formulas:

[0025] in, PI C ( s )and PI V ( s The transfer functions of the current loop and voltage loop PI controllers are respectively. L f_ES and C f_ES These are the filter inductor and filter capacitor for a grid-type energy storage converter, respectively. v vdqref+ The reference voltage generated for virtual impedance control. f VF ( s Let be the voltage feedforward transfer function. The dynamic equation for virtual impedance control is expressed by the following formula:

[0026] in, v dqref+ For the reference voltage vector, L v It is a virtual inductance.

[0027] Based on the grid-connected energy storage converter LC The dynamic equations for the filter, current control loop, voltage control loop, and virtual impedance control are used to construct a complex vector form inner-loop admittance model for the grid-type energy storage converter, expressed by the following formula:

[0028] Among them, the voltage feedforward transfer function f VF ( s It can be expressed by the following formula:

[0029] in, k VF For voltage feedforward coefficients, T VF is the filter time constant.

[0030] In step S20, please refer to Figure 1 Step S20, based on the established inner-loop admittance model, constructs the electrical equations for the output current and grid-connected point voltage of the grid-connected converter and the grid-connected converter in their respective synchronous coordinate systems when a small disturbance occurs in the grid voltage. It also establishes the transformation equations for each electrical quantity between the grid-connected coordinate system and the grid-connected coordinate system, specifically including: Since grid-connected converters and grid-mounted converters employ different synchronous control methods to track the grid phase, grid-connected renewable energy equipment and grid-mounted energy storage equipment need to implement vector control in their respective synchronous coordinate systems. Let the local synchronous coordinate system of the grid-connected renewable energy be... NE The local synchronous coordinate system of grid-type energy storage is ES And introduce a global coordinate system C It rotates at a constant rated angular velocity during minor disturbances to the power grid.

[0031] Based on the above coordinate system setting, when a small disturbance occurs in the grid voltage phase, a grid-following coordinate system is constructed. NE With the grid coordinate system ES The electrical equations relating the output current of the downconverter to the grid connection point voltage, including the grid coordinate system. NE The relationship between the output current of new energy sources and the grid connection point voltage, and the grid coordinate system. ES The relationship between the energy storage output current and the grid connection point voltage is expressed by the following formula: In the formula:

[0032] in, To determine the output current of the new energy converter in the grid coordinate system, The output current of the energy storage converter in the grid coordinate system. and These are the grid connection point voltages in the grid coordinate system and the network coordinate system, respectively. Y NE+ To establish the connection admittance between the output current of the new energy converter and the grid connection point voltage in the grid coordinate system, Y ES+ This refers to the connection admittance between the output current of the energy storage converter and the grid connection point voltage in the grid coordinate system. Z line_NE+ and Z line_ES+ These are the line impedances of grid-connected new energy converters and grid-connected energy storage converters, respectively.

[0033] Constructing the coordinate system of each electrical quantity in the grid NE With the grid coordinate system ES The transformation equations between them include the grid connection point voltage in the grid coordinate system. NE With the grid coordinate system ES The transformation equations between them, and the output currents of the grid-connected converter and the grid-connected converter in the grid coordinate system. NE With the grid coordinate system ES The transformation equation between them is expressed by the following formula:

[0034] in, The output current of the new energy converter in the grid coordinate system. To determine the output current of the energy storage converter in the grid coordinate system, V dq+ This is the steady-state value of the grid connection point voltage. I dq_NE+ and I dq_ES+ These are the steady-state values ​​of the output current of the grid-connected new energy converter and the grid-connected energy storage converter, respectively. and These are the phase disturbances of the network synchronization coordinate system and the phase disturbances of the network synchronization coordinate system, respectively.

[0035] In step S30, please refer to Figure 1 Step S30, based on the transformation equations of various electrical quantities between the grid-connected coordinate system and the network-connected coordinate system, and combined with the phase disturbances generated by the synchronous coordinate systems of the grid-connected and network-connected systems when the grid voltage phase experiences small disturbances, constructs expressions to transform the grid connection point voltage from the global coordinate system to the grid-connected coordinate system and the network-connected coordinate system, respectively. Specifically, this includes: When a small disturbance occurs in the grid voltage phase, small-signal expressions for the phase disturbance in the grid-synchronized coordinate system of new energy and the grid-connected energy storage are constructed respectively, and are expressed by the following formula:

[0036] in, and These are the phase disturbances of the network synchronization coordinate system and the phase disturbances of the network construction synchronization coordinate system, respectively. and These represent the positive and negative sequence output voltages of the new energy converter in the grid coordinate system, respectively. and These represent the positive and negative sequence output currents of the energy storage converter in the grid coordinate system; the power fluctuation of the energy storage equipment is approximately... ; k ppll and k ipll These are the proportional coefficient and integral coefficient of the phase-locked loop proportional-integral controller, respectively. V 0 represents the rated voltage. ω 0 represents the rated angular velocity; J and D p These are the inertia coefficient and damping coefficient for power synchronization control, respectively.

[0037] The grid-side circuit equations constructed in the global coordinate system are expressed by the following formula:

[0038] in, The grid connection point voltage in the global coordinate system. and These represent the output currents of the new energy converter and the energy storage converter in the global coordinate system, respectively. The grid voltage is in the global coordinate system. L g For the inductive reactance of the power grid line, Z g+ This represents the power grid impedance.

[0039] Based on the transformation equations established above for the output current of each converter and the grid connection point voltage between different coordinate systems, when a small disturbance occurs in the grid voltage phase, a transformation equation is constructed to change the grid connection point voltage from the global coordinate system. C Transform to the grid coordinate system respectively NE With the grid coordinate system ES The following expression is represented by the formula:

[0040] in, This refers to the phase disturbance of the grid voltage. V gdq+ and I gdq+ These are the steady-state values ​​of the grid voltage and grid current, respectively.

[0041] In step S40, please refer to Figure 1 Step S40, which involves constructing small-signal disturbance models for the output voltage of grid-connected new energy sources and the output current of grid-connected energy storage in their respective synchronous coordinate systems under grid voltage phase disturbances, based on the expressions of the grid connection point voltage in the grid-connected coordinate system and the grid-connected coordinate system, and combining the coordinate transformation equations of various electrical quantities, specifically includes: Based on the grid connection point voltage constructed above in the grid coordinate system NE With the grid coordinate system ES The following expression, combined with the transformation equations of the output current of each converter and the grid connection point voltage between different coordinate systems, is used to construct the grid connection point voltage in the grid coordinate system. NE With the grid coordinate system ES The following expression for the phase perturbation is given by the formula:

[0042] Based on the relationship between grid connection point voltage and new energy output voltage and energy storage output current, establish a grid-connected coordinate system. NE Small-signal perturbation model and network coordinate system of new energy output voltage ES The small-signal perturbation model of the energy storage output current is expressed by the following formula:

[0043] In the formula:

[0044] It can be seen that the synchronization phase of the two converters will affect the output voltage of the grid-connected renewable energy and the output current of the grid-connected energy storage. Changes in the output voltage of the grid-connected renewable energy will affect the grid-connected synchronization phase through the phase-locked loop, and changes in the output current of the grid-connected energy storage will affect the grid-connected synchronization phase through the power synchronization loop, thus forming a closed loop.

[0045] In step S50, please refer to Figure 1 In step S50, based on the established small-signal disturbance model, the phase angle interaction relationship between the grid voltage phase disturbance and the phase disturbance of the grid-connected and grid-connected coordinate systems is established, and a closed-loop transfer function of grid voltage phase disturbance-grid-connected energy storage phase disturbance for judging the stability of energy storage equipment is constructed, namely the synchronous dominant loop of the grid-connected energy storage converter, specifically including: Based on the established small-signal disturbance model of the grid-connected renewable energy output voltage, and combined with the small-signal expression of the phase disturbance in the grid-connected coordinate system, an interaction expression for the phase disturbance of the grid voltage and the phase disturbance in the grid-connected coordinate system is constructed, expressed by the following formula: In the formula:

[0046] in, I dq_ES- The steady-state value of the negative sequence current output by the grid-connected energy storage converter; V dq- This represents the steady-state value of the negative sequence voltage at the grid connection point. V gdq- and I gdq- These are the steady-state values ​​of the negative-sequence voltage and negative-sequence current of the power grid, respectively. For variables X . conjugate.

[0047] Based on the established small-signal disturbance model of the grid-connected energy storage output current, and combined with the small-signal expression of the phase disturbance in the grid coordinate system, the phase angle interaction expression of the grid voltage phase disturbance and the grid coordinate system phase disturbance is constructed, as shown in the following formula:

[0048] In the formula:

[0049] in, I dq_NE- This refers to the steady-state value of the negative sequence current output by the grid-connected new energy converter.

[0050] Based on the established phase angle interaction expression, a closed-loop transfer function for grid voltage phase disturbance-grid-energy storage phase disturbance, used to determine the stability of the energy storage converter, is constructed, which is the synchronous dominant loop of the grid-connected energy storage converter, and is expressed by the following formula:

[0051] in:

[0052] Based on the established closed-loop transfer function, the open-loop transfer function of the synchronous main circuit of the grid-connected energy storage converter can be obtained, expressed by the following formula:

[0053] in, L ES ( s Let be the open-loop transfer function of the system. f δ_ES ( s It integrates the electrical relationships of parallel system lines, the control loop of the grid-connected inner loop and the dynamic characteristics of the grid-connected new energy phase-locked loop, and includes information such as the stable operating point of new energy and energy storage. Therefore, it is affected by the output power of new energy. f PSC ( s The synchronous control loop of the grid-type energy storage includes the dynamic characteristics of the synchronization link and the controllable damping parameters of the energy storage. Therefore, the synchronous control loop of the grid-type energy storage converter includes the output power variable of the new energy source and the controllable damping parameters of the energy storage, which can be used to analyze the impact of the new energy output on the stability of the grid-type energy storage equipment.

[0054] In step S60, please refer to Figure 1 In step S60, based on the constructed synchronous dominant loop, a stability criterion for the grid-connected energy storage equipment is established. An objective function and parameter constraints for the virtual damping adjustment of the grid-connected energy storage near the subsynchronous oscillation frequency of the new energy storage parallel system are constructed. An optimization equation is established, and the corresponding virtual damping is calculated to adjust the damping coefficient of the virtual synchronous control of the grid-connected energy storage. Specifically, this includes: Based on the aforementioned synchronous-dominant circuit, the energy storage converter is stable if and only if f δ_ES ( s ) and 1 / f PSC ( s )exist L ES ( s The gain crossover frequency is... f δ_ES ( s ) and 1 / f PSC ( s The phase difference at points where the amplitudes are equal is less than 180°. Because the system dynamics are dynamically divided into two parts, this stability criterion can better and more intuitively analyze the interaction between the dynamics of the grid-connected energy storage power synchronization loop and the dynamics of grid-connected new energy equipment, and reveal the corresponding instability mechanism.

[0055] Based on the synchronous dominant circuit containing the output power component of new energy sources. f δ_ES (s ) and energy storage synchronization loop components f PSC ( s The objective function and parameter constraints of the virtual damping regulation of the new energy grid-connected system and the parallel grid-type energy storage near the subsynchronous oscillation frequency of the new energy storage are constructed, and the optimization equation is established, expressed by the following formula:

[0056] in, f SSO The subsynchronous oscillation angular frequency, f SSO_N The subsynchronous oscillation frequency under rated operating conditions. PM The phase margin is given; if the output of new energy decreases, the change in the subsynchronous oscillation frequency is within 2Hz. Therefore, the constraint is that the subsynchronous oscillation frequency under rated operating conditions is within ±2Hz. Based on this optimization equation, the corresponding virtual damping parameters are calculated to adjust the damping coefficient of the virtual synchronous control link of the grid-type energy storage, thereby suppressing the risk of subsynchronous oscillation under the fluctuation of new energy output.

[0057] Experimental verification: Figure 3 The simulation waveform of the output frequency of the grid-connected energy storage under the condition of energy output fluctuation is shown when the control method of the present invention is used in a parallel system of grid-connected new energy and grid-connected energy storage. It can be seen that the control method of the present invention can adaptively optimize the virtual damping parameters of the grid-connected energy storage according to the output state of the new energy, suppress the frequency oscillation of the grid-connected energy storage when the output of the new energy decreases, and improve the operational stability of the parallel system of grid-connected new energy and grid-connected energy storage.

[0058] Finally, it should be noted that the above embodiments are merely illustrative of the technical solutions of the present invention and not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the specific embodiments of the present invention, but such modifications or alterations are all within the scope of protection of the pending claims.

Claims

1. A damping control method for grid-type energy storage applicable to fluctuations in new energy output, characterized in that, The control method includes: S10: By establishing the filter dynamic equations and inner loop control loop dynamic equations for grid-connected new energy converters and grid-connected energy storage converters respectively, an inner loop admittance model for grid-connected new energy converters and grid-connected energy storage converters is constructed. S20: Based on the established inner loop admittance model, when the grid voltage phase is slightly disturbed, the electrical equations of the output current and grid connection point voltage of the grid-connected converter and the grid-connected converter in their respective synchronous coordinate systems are constructed, and the transformation equations of each electrical quantity between the grid-connected coordinate system and the grid-connected coordinate system are established. S30: Based on the transformation equations of each electrical quantity between the grid-connected coordinate system and the grid-connected coordinate system, and combined with the phase disturbance generated by the synchronous coordinate system of the grid-connected and grid-connected systems when the grid voltage phase undergoes a small disturbance, an expression is constructed to transform the grid connection point voltage from the global coordinate system to the grid-connected coordinate system and the grid-connected coordinate system respectively. S40: Based on the expression of the grid connection point voltage in the grid-connected coordinate system and the grid-connected coordinate system, and combined with the coordinate transformation equations of various electrical quantities, construct small-signal disturbance models of the grid-connected new energy output voltage and the grid-connected energy storage output current in their respective synchronous coordinate systems when the grid voltage phase disturbance occurs. S50: Based on the established small-signal disturbance model, establish the phase angle interaction relationship between the grid voltage phase disturbance and the phase disturbance of the grid-connected and grid-connected coordinate systems, respectively, and construct the grid voltage phase disturbance-grid-connected energy storage phase disturbance closed-loop transfer function for judging the stability of energy storage equipment, that is, the synchronous dominant loop of the grid-connected energy storage converter. S60: Based on the constructed synchronous dominant loop, establish the stability criteria for grid-connected energy storage equipment, construct the objective function and parameter constraints for virtual damping adjustment of grid-connected energy storage near the subsynchronous oscillation frequency of the new energy storage parallel system, establish the optimization equation, and calculate the corresponding virtual damping to adjust the damping coefficient of the virtual synchronous control of grid-connected energy storage.

2. The damping control method for grid-type energy storage under fluctuating new energy output as described in claim 1, characterized in that, Step S10 includes: In the controller dq Construct in coordinate system LC The dynamic equations of the filter; constructing the dynamic equations of the current control loop of the grid-connected new energy converter, combined with... LC The dynamic equations of the filter are used to establish a complex vector form inner-loop admittance model for the grid-connected new energy converter; the dynamic equations of the current control loop, voltage control loop, and virtual impedance control of the grid-connected energy storage converter are constructed, combined with... LC The dynamic equations of the filter are used to establish a complex vector form inner-loop admittance model for the grid-connected energy storage converter.

3. The damping control method for grid-type energy storage under fluctuating new energy output as described in claim 1, characterized in that, Step S20 includes: Based on the established inner-loop admittance models of grid-connected renewable energy converters and grid-connected energy storage converters, when small disturbances occur in the grid voltage, electrical equations are constructed for the output current of the converters and the grid connection point voltage in the grid-connected coordinate system and the grid-connected coordinate system. The electrical equations include the relationship between the renewable energy output current and the grid connection point voltage in the grid-connected coordinate system, and the relationship between the energy storage output current and the grid connection point voltage in the grid-connected coordinate system. Transformation equations for each electrical quantity between the grid-connected coordinate system and the grid-connected coordinate system are also established, including the transformation equations for the grid connection point voltage, the output current of the grid-connected converter, and the output current of the grid-connected converter between the grid-connected coordinate system and the grid-connected coordinate system, respectively.

4. The damping control method for grid-type energy storage under fluctuating new energy output as described in claim 1, characterized in that, Step S30 includes: When a small disturbance occurs in the phase of the grid voltage, small-signal expressions for the phase disturbance in the synchronous coordinate system of grid-connected new energy and the synchronous coordinate system of grid-connected energy storage are constructed respectively. Combined with the established transformation equations of the grid connection point voltage and the output current of each converter between different coordinate systems, and combined with the grid-side circuit equations in the global coordinate system, expressions are constructed to transform the grid connection point voltage from the global coordinate system to the grid-connected coordinate system and the grid-connected coordinate system respectively.

5. The damping control method for grid-type energy storage under fluctuating new energy output as described in claim 1, characterized in that, Step S40 includes: Based on the constructed expressions for the grid connection point voltage in the grid-following coordinate system and the grid-building coordinate system, and combined with the transformation equations of the grid connection point voltage and the output current of each converter between different coordinate systems, expressions for the phase disturbance of the grid connection point voltage in the grid-following coordinate system and the grid-building coordinate system are constructed respectively. Based on the relationship between the grid connection point voltage and the output voltage of new energy and the output current of energy storage, small-signal disturbance models of the output voltage of new energy in the grid-following coordinate system and small-signal disturbance models of the output current of energy storage in the grid-building coordinate system are established.

6. The damping control method for grid-type energy storage under fluctuating new energy output as described in claim 1, characterized in that, Step S50 includes: Based on the established small-signal disturbance model of the grid-connected renewable energy output voltage, and combined with the small-signal expression of the phase disturbance in the grid-connected coordinate system, an interaction expression of the phase angle between the grid voltage phase disturbance and the grid-connected coordinate system phase disturbance is constructed. Based on the established small-signal disturbance model of the grid-connected energy storage output current, and combined with the small-signal expression of the phase disturbance in the grid-connected coordinate system phase disturbance, an interaction expression of the phase angle between the grid voltage phase disturbance and the grid-connected coordinate system phase disturbance is constructed. Combining the two interaction expressions, a closed-loop transfer function of grid voltage phase disturbance-grid-connected energy storage phase disturbance for judging the stability of the energy storage converter is constructed, which is the synchronous dominant loop of the grid-connected energy storage converter.

7. The damping control method for grid-type energy storage under fluctuating new energy output as described in claim 1, characterized in that, Step S60 includes: Based on the aforementioned synchronous dominant loop, the open-loop transfer function of the grid-connected energy storage converter is obtained, and the system is dynamically divided into two parts to establish a stability criterion for the system. Based on this stability criterion, an objective function for virtual damping adjustment of the new energy grid-connected system and the parallel grid-connected energy storage near the subsynchronous oscillation frequency of the new energy storage system is constructed, along with the parameter constraints of the objective function. An optimization equation is established, and the virtual damping amount corresponding to suppressing the subsynchronous oscillation risk under the fluctuation of new energy output is calculated to adjust the damping coefficient of the virtual synchronous control link of the grid-connected energy storage system.

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