A network-constructed energy storage positive and negative sequence decoupling three-phase unbalance compensation method

Abstract

This invention discloses a method for decoupling positive and negative sequence three-phase imbalance compensation in grid-connected energy storage, relating to the field of energy storage converter control technology. This method collects relevant operating parameters of the grid-connected energy storage and the distribution area, extracts the positive and negative sequence voltage components at the grid connection point, and establishes a positive sequence grid-connection maintenance control channel and a negative sequence adaptive admittance compensation channel, respectively. The negative sequence compensation current command is sequentially corrected for second-harmonic power oscillation suppression and capacity constraints, generating a three-phase modulation command to drive the converter to perform compensation. The control parameters are adaptively adjusted through closed-loop feedback. This invention achieves complete decoupling of positive sequence grid connection and negative sequence compensation, efficiently completing three-phase imbalance compensation in the distribution area while prioritizing the voltage build-up, frequency stabilization, and inertia support capabilities of the grid-connected energy storage, thus improving the system's adaptability and stability under different operating conditions.

Description

Technical Field

[0001] This invention relates to the field of energy storage converter control technology, specifically to a three-phase imbalance compensation method for positive and negative sequence decoupling in grid-type energy storage. Background Technology

[0002] With the large-scale integration of distributed photovoltaic power, electric vehicle charging loads, and single-phase residential loads into low-voltage distribution substations, the three-phase load distribution in these substations is becoming increasingly uneven. Three-phase imbalance leads to phase voltage deviation, increased equipment heating, and increased line losses, severely impacting the reliability and power quality of the substation's power supply. This problem is particularly prominent in weak grid operation and high-penetration scenarios involving distributed renewable energy, and has become one of the key factors restricting the safe and stable operation of low-voltage distribution networks.

[0003] Currently, several technical solutions exist for three-phase imbalance compensation in transformer substations using energy storage. For example, invention patent publication number CN117318126B discloses an integrated device and control method for microgrid power quality optimization and energy storage, which achieves three-phase imbalance compensation through an energy storage converter; another invention patent publication number CN114552608B discloses a three-phase imbalance mitigation method based on the charging and discharging of an energy storage system, which balances the three-phase load by adjusting the charging and discharging current of each phase. These methods can improve the three-phase imbalance situation in transformer substations to a certain extent.

[0004] However, existing technologies generally suffer from a technical problem: negative-sequence compensation control is usually directly superimposed on the positive-sequence voltage-building main loop of grid-type energy storage, resulting in severe coupling interference between the two. When negative-sequence compensation is activated, it inevitably affects the stability of positive-sequence grid-type control, weakening the voltage-building, frequency stabilization, and inertia support capabilities of grid-type energy storage. Especially under weak grid conditions, this coupling effect can lead to system oscillations or even instability.

[0005] Therefore, there is an urgent need to develop a three-phase imbalance compensation method that can completely decouple positive-sequence grid construction and negative-sequence compensation, so as to efficiently address the three-phase imbalance problem in the transformer area without affecting the core support capacity of grid-type energy storage. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage. By constructing a control architecture with separate channels for positive sequence grid construction and negative sequence compensation, and combining negative sequence adaptive admittance adjustment, second harmonic power oscillation suppression, and grid-priority capacity coordination mechanism, this method can efficiently complete three-phase imbalance compensation in the distribution area while prioritizing the voltage building, frequency stabilization, and inertia support capabilities of grid-type energy storage, thereby improving the system's adaptability and stability under different operating conditions.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: On one hand, a method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage, the method comprising the following steps: S1 collects the three-phase voltage, three-phase current, DC bus voltage, energy storage state of charge, positive sequence active power, positive sequence reactive power, rated capacity of energy storage converter, and short-circuit ratio of the distribution area at the grid-connected point of the grid-type energy storage. S2, based on the positive sequence grid angle of grid-type energy storage, adopts a dual synchronous rotating coordinate system positive and negative sequence separation algorithm to extract the positive sequence voltage component and negative sequence voltage component at the grid connection point; S3, establish a positive sequence grid-building maintenance control channel based on the positive sequence voltage component, and generate a positive sequence grid-building voltage command; S4, establish a negative sequence adaptive admittance compensation channel based on the negative sequence voltage component, and generate a negative sequence compensation current command; S5, extract the second harmonic power component from the instantaneous active power of the grid-type energy storage, and perform oscillation suppression correction on the negative sequence compensation current command according to the amplitude of the second harmonic power. S6, calculate the remaining capacity based on the rated capacity of the energy storage converter and the positive sequence grid capacity occupancy, and perform capacity constraint correction on the negative sequence compensation current command based on the remaining capacity; S7 transforms the positive-sequence grid voltage command and the negative-sequence compensation current command after capacity constraint to the three-phase stationary coordinate system to generate a three-phase modulation command. S8, the three-phase modulation command is executed through the grid-type energy storage converter to achieve three-phase imbalance compensation; S9 calculates the compensated voltage imbalance, current imbalance, and second harmonic power fluctuation in real time, and adaptively corrects the negative sequence virtual admittance parameter and second harmonic suppression coefficient based on the feedback results.

[0008] By constructing a control architecture with positive-sequence grid construction and negative-sequence compensation channels, and combining negative-sequence adaptive admittance adjustment, second-harmonic power oscillation suppression, and capacity coordination mechanisms, the system can efficiently complete three-phase imbalance compensation in the distribution area while prioritizing the voltage building, frequency stabilization, and inertia support capabilities of grid-type energy storage. At the same time, the system improves its adaptability and stability under different operating conditions by optimizing control parameters in real time through closed-loop feedback.

[0009] Furthermore, in step S2, the three-phase voltage and current are first transformed by Clarke to obtain the components in the stationary coordinate system, and then transformed to the positive-sequence synchronous rotating coordinate system and the negative-sequence synchronous rotating coordinate system based on the positive-sequence grid angle, respectively. The transformed components are then low-pass filtered to obtain the positive-sequence voltage component and the negative-sequence voltage component, and a double-frequency cross decoupling stage is used to suppress the coupling disturbance between the positive and negative sequences.

[0010] A dual-synchronous rotating coordinate system separation method based on the positive-sequence grid angle of the grid-type energy storage is adopted, which does not rely on an external phase-locked loop and can effectively adapt to weak grid operating environments. Combined with low-pass filtering and second-harmonic cross-decoupling, the positive-sequence and negative-sequence voltage components can be accurately extracted, and the coupling disturbances between components can be suppressed, providing reliable basic data for subsequent channel-specific control.

[0011] Furthermore, in step S3, the positive sequence grid-keeping control channel achieves active-frequency regulation through virtual inertia and virtual damping, maintains system frequency stability and provides inertia support, and generates positive sequence grid voltage amplitude through reactive-voltage coordinated regulation, and obtains the final positive sequence grid voltage command by combining the positive sequence grid angle.

[0012] The positive-sequence grid-maintaining control channel achieves active-frequency regulation through virtual inertia and virtual damping, which can provide necessary inertia support for the system and smooth frequency fluctuations. At the same time, it generates positive-sequence grid-connected voltage commands by adopting a reactive-voltage coordinated regulation method, which can stabilize the grid connection point voltage and ensure that the grid-connected energy storage always maintains the dominant position of the positive-sequence voltage source.

[0013] Furthermore, in step S4, the negative sequence compensation current command is generated by superimposing three parts: The first part is based on the generation of the product of negative-sequence adaptive virtual admittance and negative-sequence voltage; The second part is based on the generation of the proportional suppression term of the negative sequence current; The third part is the generation of dynamic damping terms based on negative sequence current.

[0014] The negative sequence compensation current command is generated by superimposing an adaptive admittance term, a proportional suppression term, and a dynamic damping term. It can quickly respond to changes in negative sequence voltage and current, effectively suppress the dynamic oscillation of negative sequence current, improve the response speed and stability of negative sequence compensation, and avoid the adjustment lag or overshoot problems caused by single proportional compensation.

[0015] Furthermore, the negative-sequence adaptive virtual admittance is based on the basic negative-sequence admittance and is adjusted online according to the ratio of negative-sequence voltage to positive-sequence voltage, the ratio of negative-sequence current to positive-sequence current, and the short-circuit ratio of the transformer area. When the negative-sequence voltage increases, the negative-sequence current increases, or the short-circuit ratio of the transformer area decreases, the negative-sequence adaptive virtual admittance automatically increases.

[0016] The negative-sequence adaptive virtual admittance is based on the basic admittance and is adjusted online by combining the ratio of negative-sequence voltage to positive-sequence voltage, the ratio of negative-sequence current to positive-sequence current, and the short-circuit ratio of the transformer area. It can automatically match different unbalance levels and grid strength to achieve accurate negative-sequence compensation and avoid over-compensation or under-compensation caused by fixed compensation coefficients.

[0017] Furthermore, in step S5, the instantaneous active power of the grid-type energy storage is decomposed into a DC component and a second harmonic AC component. The amplitude of the second harmonic AC component is calculated, and a second harmonic suppression coefficient is generated based on the upper limit of the second harmonic power. This coefficient is used to proportionally correct the negative sequence compensation current command and limit the amplitude of the second harmonic power oscillation.

[0018] By decomposing the instantaneous active power of the grid-type energy storage system, extracting the second harmonic component, and calculating its amplitude, and generating a suppression coefficient based on the preset power upper limit to proportionally correct the negative sequence compensation current, the amplitude of the second harmonic power oscillation can be effectively limited without completely interrupting the negative sequence compensation, thereby reducing its impact on the DC bus voltage and improving the stability of system operation.

[0019] Furthermore, in step S6, the positive sequence grid capacity occupancy is first calculated based on the positive sequence active power and positive sequence reactive power, and then the remaining capacity is calculated in combination with the rated capacity of the energy storage converter. When the capacity required for negative order compensation is less than or equal to the remaining capacity, perform full negative order compensation. When the required capacity for negative sequence compensation is greater than the remaining capacity, the negative sequence compensation current command is limited and corrected according to the ratio of the remaining capacity to the required compensation capacity.

[0020] A capacity coordination mechanism prioritizing network construction is adopted. First, the capacity required for positive-sequence network construction is calculated, and then the remaining capacity is used to perform negative-sequence compensation. When the compensation demand exceeds the remaining capacity, the compensation current is limited proportionally. This ensures that the network support capacity is not affected, converter resources are allocated reasonably, and system failures caused by capacity overruns are avoided.

[0021] Furthermore, in step S7, the positive-sequence grid voltage command and the negative-sequence compensation current command after capacity constraint are first inversely transformed to the three-phase stationary coordinate system, and then the positive-sequence voltage deviation is adjusted by the grid voltage controller and the negative-sequence current deviation is adjusted by the negative-sequence current controller. The outputs of the two controllers are superimposed to obtain the three-phase modulation command.

[0022] By inversely transforming the positive-sequence grid voltage command and the negative-sequence compensation current command to the three-phase stationary coordinate system, and then superimposing them after adjustment by independent voltage and current controllers to generate modulation commands, the positive-sequence voltage control and negative-sequence current control can be completely decoupled, avoiding mutual interference between the two and improving the accuracy of the modulation signal and the control effect.

[0023] Furthermore, in step S9, the voltage imbalance is the ratio of the negative sequence voltage amplitude to the positive sequence voltage amplitude, and the current imbalance is the ratio of the negative sequence current amplitude to the positive sequence current amplitude. Using voltage imbalance, current imbalance, and second harmonic power amplitude as feedback quantities, the correction coefficients of the negative sequence virtual admittance and the upper limit of the second harmonic power are adjusted online.

[0024] Using voltage imbalance, current imbalance, and second harmonic power amplitude as feedback quantities, the correction coefficient of negative sequence virtual admittance and the upper limit of second harmonic power are adjusted online. This allows for real-time optimization of control parameters based on the actual operating status of the system, maintaining a good three-phase imbalance compensation effect and adapting to dynamic changes in transformer area load and grid conditions.

[0025] On the other hand, a grid-type energy storage positive and negative sequence decoupled three-phase imbalance compensation system is applicable to a grid-type energy storage positive and negative sequence decoupled three-phase imbalance compensation method. The system comprises: The data acquisition module is used to collect three-phase voltage, three-phase current, DC bus voltage, energy storage state of charge, converter capacity, and transformer area short-circuit ratio at the grid connection point. The positive and negative sequence separation module is used to extract the positive and negative sequence voltage components based on the positive sequence grid angle of the grid-type energy storage. The positive sequence grid-building maintenance module is used to generate positive sequence grid-building voltage commands to achieve voltage build-up, frequency stabilization, and inertia support. The negative sequence adaptive admittance compensation module is used to generate negative sequence compensation current commands based on negative sequence voltage, negative sequence current and transformer area short-circuit ratio; The second harmonic power observation and suppression module is used to extract the second harmonic power component from the instantaneous active power and correct the negative sequence compensation current command according to the second harmonic power amplitude. The capacity coordination module is used to generate executable negative-sequence compensation current commands based on the positive-sequence grid capacity occupancy and the rated capacity of the energy storage converter. The modulation instruction generation module is used to combine the positive-sequence grid voltage instruction and the executable negative-sequence compensation current instruction into a three-phase modulation instruction; The converter execution module is used to drive the grid-type energy storage converter to output compensation voltage and compensation current; The feedback correction module is used to adaptively correct the negative sequence virtual admittance parameter and the second harmonic suppression coefficient based on the compensated voltage imbalance, current imbalance and second harmonic power fluctuation.

[0026] This method also includes a system that integrates functional modules such as data acquisition, positive and negative sequence separation, positive sequence network maintenance, negative sequence adaptive compensation, second harmonic oscillation suppression, capacity coordination, modulation generation, and feedback correction. It can fully execute the above three-phase imbalance compensation method. Each module has a clear division of labor and works in concert, ensuring stable and reliable operation. It is suitable for various complex operating scenarios in low-voltage distribution substations.

[0027] Compared with existing technologies, this method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage has the following advantages: I. This invention constructs a dual-control channel architecture that completely decouples positive-sequence grid construction and negative-sequence compensation. It employs a positive-negative sequence separation algorithm based on the positive-sequence grid construction angle of the grid-type energy storage system, coupled with independent positive-sequence voltage and negative-sequence current controllers, to achieve complete decoupling of positive-sequence grid construction control and negative-sequence compensation control. This completely eliminates the coupling interference of negative-sequence compensation on the positive-sequence grid construction main loop. Even when negative-sequence compensation is in operation, the grid-type energy storage system maintains its voltage build-up, frequency stabilization, and inertia support capabilities, effectively improving the system's operational stability in weak grid and high-renewable energy penetration scenarios, and avoiding system oscillations and instability caused by coupling effects.

[0028] II. This invention employs a negative-sequence adaptive virtual admittance adjustment mechanism, combined with second-harmonic power oscillation suppression and a grid-priority capacity coordination strategy, while introducing closed-loop feedback to correct control parameters in real time. It can automatically match different degrees of three-phase imbalance conditions and grid strength, accurately achieving negative-sequence compensation, avoiding over-compensation and under-compensation, effectively suppressing second-harmonic power oscillations and DC bus voltage fluctuations generated during negative-sequence compensation, rationally allocating converter capacity resources, improving the system's adaptability to dynamic operating conditions, and ensuring the continuity and reliability of three-phase imbalance compensation effects.

[0029] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0031] Figure 1 This is a flowchart of the overall process for three-phase imbalance compensation of grid-type energy storage based on positive and negative sequence separation according to the present invention. Figure 2 This is a schematic diagram illustrating the principle of positive and negative sequence separation in the dual synchronous rotating coordinate system of the present invention. Figure 3 This is a structural diagram of the negative-order adaptive admittance compensation and second harmonic power suppression of the present invention. Detailed Implementation

[0032] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0033] Example This embodiment provides a method and system for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage, applied to a low-voltage distribution substation grid-type energy storage system with a rated capacity of 100kVA. The system adopts a three-phase four-bridge topology, with a DC bus rated voltage of 750V, a substation rated line voltage of 380V, and a rated frequency of 50Hz. This embodiment constructs a dual-control channel architecture that completely decouples positive-sequence grid construction and negative-sequence compensation. Combined with positive- and negative-sequence separation based on grid angle, negative-sequence adaptive admittance adjustment, second-harmonic power oscillation suppression, and a capacity coordination mechanism prioritizing grid construction, it achieves efficient management of three-phase imbalance in the substation while prioritizing the voltage build-up, frequency stabilization, and inertia support capabilities of the grid-type energy storage. Experimental results show that under the condition of an initial voltage imbalance of 15% in the substation, this method can suppress the voltage imbalance to below 2%, control the second-harmonic power fluctuation amplitude to within 3kW, and ensure stable and reliable system operation.

[0034] Specifically, refer to Figure 1 As shown, the compensation system used in this embodiment consists of a grid-type energy storage converter, a data acquisition unit, a three-phase imbalance compensation controller, and an equivalent unit of the distribution grid and load. The components form a complete signal acquisition, control calculation, drive execution, and feedback correction path, which can stably support the complete implementation of the compensation method described in this invention.

[0035] Understandable, Figure 1 As a schematic diagram of the overall architecture of this invention, it clearly illustrates the entire process from three-phase voltage and current sampling, positive and negative sequence separation, positive sequence network holding control, negative sequence adaptive admittance compensation, second harmonic power suppression, capacity coordination limiting, to the final modulation output and feedback correction. This architecture provides clear physical support and execution path for the implementation of the method of this invention from both hardware structure and control flow perspectives, ensuring that the method steps can reliably operate based on actual physical systems.

[0036] Specifically, the grid-connected energy storage converter adopts a three-phase four-arm topology, consisting of battery clusters, DC bus capacitors, IGBT power modules, filter inductors L and C. The battery clusters are connected to the DC side of the converter via the DC bus, providing active power support for the system; the AC side of the converter is connected to the grid connection point PCC via filter inductors and filter capacitors, realizing energy exchange with the grid.

[0037] The data acquisition unit includes voltage sensors, current sensors, and a battery management system (BMS) for real-time acquisition of operating parameters such as three-phase voltage, three-phase current, DC bus voltage, and state of charge (SOC) of the energy storage at the grid connection point.

[0038] The three-phase imbalance compensation controller is implemented using a digital signal processor (DSP) with a sampling frequency of 10kHz and a control period of 100μs. The controller integrates a positive-sequence separation module, a positive-sequence network holding module, a negative-sequence adaptive admittance compensation module, a second harmonic power observation and suppression module, a capacity coordination module, a modulation command generation module, and a feedback correction module. These modules work together to complete all the control functions for three-phase imbalance compensation.

[0039] In this embodiment, the detailed implementation steps are as follows: S1, Data Acquisition Operation: The data acquisition unit collects the operating parameters of the grid-type energy storage system in real time, providing basic data for subsequent control. The specific parameters collected include: Three-phase voltage at grid connection point The voltage is acquired using a Hall effect voltage sensor, with a measurement range of 0–500V and an accuracy of 0.5%. Three-phase current at grid connection point The measurement is conducted using a Hall current sensor, with a measurement range of 0–200A and an accuracy of 0.5%. DC bus voltage The voltage is acquired using a resistive voltage divider sensor, with a measurement range of 0–1000V and an accuracy of 0.5%. Energy storage state of charge (SOC): provided by the energy storage management system (BMS), with an update frequency of 1Hz; Positive sequence active power of energy storage and positive sequence reactive power : Calculated in real time by the controller based on the positive sequence voltage component; Rated capacity of energy storage converter System preset parameters, in this embodiment ; The short-circuit ratio (SCR) of the transformer area is calculated in real time using an online impedance identification method with a calculation period of 1 second.

[0040] For example, the online impedance identification method employs the small-signal disturbance injection method. This involves injecting a small-signal voltage disturbance with an amplitude of 1% of the rated voltage and a frequency of 75Hz into the converter control. By measuring the current response at the grid connection point, the equivalent impedance of the transformer substation is calculated, and subsequently, the short-circuit ratio of the substation is determined. ,in This is the rated voltage of the transformer substation. This is the equivalent impedance of the transformer area.

[0041] The acquired analog signals are converted into digital signals by a 16-bit A / D converter and then sent to the controller for processing. To suppress high-frequency noise interference, the acquired voltage and current signals are first subjected to a first-order low-pass filter with a cutoff frequency of 2kHz.

[0042] S2, extraction of positive and negative sequence voltage components: Reference Figure 2 As shown, the positive sequence grid angle generated by the grid-type energy storage itself. A dual-synchronous rotating coordinate system positive and negative sequence separation algorithm is used to extract the positive and negative sequence voltage components of the grid-connected point voltage and current. The specific steps are as follows: Clarke Transform: Transforms the voltage and current components in a three-phase stationary coordinate system to a two-phase stationary coordinate system. In the coordinate system, the transformation formula is:

[0043] Where x represents the grid connection point voltage or current, The voltage / current components along the α-axis are given in the two-phase stationary αβ coordinate system. The β-axis voltage / current components are in a two-phase stationary αβ coordinate system. The voltage / current of phase A in a three-phase stationary abc coordinate system. The voltage / current of phase B in a three-phase stationary abc coordinate system. The voltage / current of phase C is given in the three-phase stationary abc coordinate system.

[0044] Understandably, the Clarke transform converts three-phase AC signals into two-phase AC signals, reducing computational complexity while maintaining the amplitude and phase information of the signal. In this embodiment, the Clarke transform employs the equal amplitude transformation principle to ensure that the amplitude of the signal is equal before and after the transformation.

[0045] Synchronous rotational transformation: using the positive sequence grid angle generated by the grid-type energy storage itself. For the synchronization angle, respectively The transformation formulas for transforming components from the original coordinate system to the positive-sequence synchronous rotating coordinate system and the negative-sequence synchronous rotating coordinate system are as follows:

[0046]

[0047] in, These are the dq-axis voltage / current components in a positive-sequence synchronous rotating coordinate system. For the dq-axis voltage / current components in the negative-sequence synchronous rotating coordinate system, the synchronous rotation transformation matrix is... ,in, For synchronous rotation transformation matrix, Let be the synchronization angle of the rotating coordinate system. The cosine value of angle θ. This is the sine value of angle θ.

[0048] In related technologies, positive and negative sequence separation typically relies on an external phase-locked loop (PLL) to obtain the phase information of the grid voltage. However, in weak grid operating environments, the grid voltage experiences significant fluctuations and distortions, making the PLL prone to lockout and resulting in inaccurate positive and negative sequence separation. This invention uses the positive sequence grid-connection angle generated by the grid-type energy storage itself as the synchronization angle, eliminating the need for an external PLL. This effectively adapts to weak grid operating environments and improves the stability and accuracy of positive and negative sequence separation.

[0049] Low-pass filtering and second harmonic crossover decoupling: The components in the positive-sequence and negative-sequence synchronous rotating coordinate systems are low-pass filtered separately to extract the DC components, which are the positive-sequence voltage components and the negative-sequence voltage components.

[0050]

[0051] in, This represents the low-pass filter function. This represents the positive-sequence dq-axis DC component obtained after filtering, i.e., the steady-state dq-axis component of the positive-sequence voltage / current. This refers to the negative-sequence dq-axis DC component obtained after filtering, which is the steady-state dq-axis component of the negative-sequence voltage / current.

[0052] In this embodiment, a first-order Butterworth filter is used as the low-pass filter, with a cutoff frequency of 10Hz. A cutoff frequency of 10Hz is chosen because the frequency of the second harmonic component is 100Hz, and a 10Hz cutoff frequency can effectively filter out the second harmonic component while ensuring a fast response to the DC component. If the cutoff frequency is too high, the second harmonic component will not be completely filtered out; if the cutoff frequency is too low, it will increase the system's response delay.

[0053] It should be noted that in the dual-synchronous rotating coordinate system, the positive-sequence voltage component, after being transformed to the positive-sequence dq coordinate system, becomes a DC component, while the negative-sequence voltage component exhibits a second-harmonic AC component; conversely, the negative-sequence voltage component, after being transformed to the negative-sequence dq coordinate system, becomes a DC component, while the positive-sequence voltage component exhibits a second-harmonic AC component. Therefore, low-pass filtering alone cannot completely eliminate the coupling interference between the positive and negative-sequence voltage components. To address this issue, this embodiment introduces a second-harmonic cross-decoupling stage to cancel out the second-harmonic components in the other coordinate system, thereby achieving accurate separation of the positive and negative-sequence voltage components.

[0054] Specifically, the implementation method of the second harmonic cross-decoupling stage is as follows: in the positive-sequence separation branch, the second harmonic component in the negative-sequence dq coordinate system is introduced as feedforward compensation; in the negative-sequence separation branch, the second harmonic component in the positive-sequence dq coordinate system is introduced as feedforward compensation. In this way, the coupling interference between the positive and negative-sequence voltage components can be suppressed to a minimum.

[0055] S3, Generation of positive sequence grid voltage command: A grid-building maintenance control loop is constructed in the positive-sequence control channel to generate positive-sequence grid-building voltage commands, thereby achieving voltage build-up, frequency stabilization, and inertia support functions. The positive-sequence grid-building maintenance control loop consists of an active power-frequency regulation link and a reactive power-voltage regulation link.

[0056] Active power-frequency regulation: Coordinated control of active power and frequency is achieved through virtual inertia and virtual damping, maintaining system frequency stability and providing inertia support. The control equation is:

[0057]

[0058] in, The derivative of the positive-sequence meshing angle with respect to time is the output angular frequency of the meshing. The positive-sequence grid angle refers to the phase angle of the positive-sequence voltage output by the grid-type energy storage. The output angular frequency of the grid-type energy storage is denoted by M, which is the virtual inertia used to simulate the rotational inertia characteristics of a synchronous generator. The derivative of the angular frequency of the network with respect to time, i.e., angular acceleration, This is the active power reference setting value. The measured value of positive-sequence active power is given, and D is the virtual damping coefficient used to suppress system frequency oscillations. The system's rated angular frequency is 314 rad / s.

[0059] The virtual inertia M simulates the rotational inertia of a synchronous generator. When the system frequency changes, it suppresses rapid frequency changes by altering the active power output of the stored energy. The virtual damping D simulates the damping winding of a synchronous generator, suppressing system oscillations. In this embodiment, the virtual inertia... Virtual damping The parameters are selected based on the following criteria: Excessive virtual inertia will slow down the system response; insufficient virtual inertia will cause excessive frequency fluctuations in the system. Excessive virtual damping will result in overly strong damping and a slow response; insufficient virtual damping will make the system prone to oscillation.

[0060] Reactive power-voltage regulation: A coordinated voltage-reactive power regulation method is adopted to generate the positive-sequence grid voltage amplitude. The control equation is:

[0061] in, Rated voltage amplitude ( ), This is the reactive power droop factor. This is the voltage regulation coefficient. This is the reactive power reference value. This is positive sequence reactive power. For reference voltage, This is the positive sequence voltage amplitude. This is the positive sequence grid voltage amplitude command, i.e., the amplitude setting value of the positive sequence voltage.

[0062] In this embodiment, the reactive power droop coefficient Voltage regulation coefficient The reactive power droop factor is used to achieve even distribution of reactive power. When multiple grid-connected energy storage units are operating in parallel, a reasonable distribution of reactive power can be achieved by using the same reactive power droop factor. The voltage regulation factor is used to improve the accuracy of voltage control and reduce voltage steady-state error.

[0063] Synthesize the positive-sequence grid-forming voltage command: Combine the positive-sequence grid-forming voltage amplitude with the positive-sequence grid-forming angle to generate the final positive-sequence grid-forming voltage command.

[0064] Through the aforementioned control methods, grid-connected energy storage can simulate the external characteristics of a synchronous generator, providing necessary voltage and frequency support to the system during grid faults or load fluctuations, ensuring stable system operation. Even in the presence of three-phase imbalance, the positive-sequence grid control loop can still operate independently, maintaining the dominant position of the positive-sequence voltage source.

[0065] S4, negative sequence compensation current command generation: Reference Figure 3 As shown, an adaptive admittance compensation model is established in the negative-sequence control channel to generate a negative-sequence compensation current command. The negative-sequence compensation current command is generated by superimposing three parts: an adaptive admittance term, a proportional suppression term, and a dynamic damping term. The control equation is:

[0066] in, This is a negative sequence compensation current command. For negative-order adaptive virtual admittance, It is a negative sequence voltage. It is a negative sequence current. The negative order proportional suppression coefficient. It is the negative-sequence dynamic damping coefficient. This is the derivative of the negative sequence current with respect to time, i.e., the instantaneous rate of change of the negative sequence current.

[0067] In this embodiment, the negative order ratio suppression coefficient Negative sequence dynamic damping coefficient The proportional suppression term improves the steady-state accuracy of negative sequence current control, while the dynamic damping term suppresses the dynamic oscillation of negative sequence current and improves system stability.

[0068] To enable the compensation model to adapt to different degrees of imbalance and grid strength, the negative-sequence adaptive virtual admittance is designed to be online adjustable. Based on the baseline negative-sequence admittance, it is adaptively adjusted according to the ratio of negative-sequence voltage to positive-sequence voltage, the ratio of negative-sequence current to positive-sequence current, and the short-circuit ratio of the transformer substations. The calculation equation is as follows:

[0069] in, Based on the negative-order admittance , , These are the negative sequence voltage coefficient, negative sequence current coefficient, and short-circuit ratio correction coefficient, respectively. SCR is the short-circuit ratio of the transformer substation. To prevent small positive numbers with a denominator of zero ( ).

[0070] In this embodiment, the basic negative-order admittance Negative sequence voltage coefficient Negative sequence current coefficient Short-circuit ratio correction factor The physical meanings of each coefficient are as follows: Negative sequence voltage coefficient When the negative sequence voltage increases, it indicates that the three-phase imbalance in the transformer area is aggravated, and it is necessary to increase the negative sequence virtual admittance and improve the negative sequence compensation capability. Negative sequence current coefficient When the negative sequence current increases, it indicates that the negative sequence load is increasing, and it is necessary to increase the negative sequence virtual admittance to absorb more negative sequence current. Short-circuit ratio correction factor When the short-circuit ratio of the transformer substation decreases, it indicates that the grid strength is weakening and the sensitivity of negative-sequence voltage to negative-sequence current is increasing. Therefore, it is necessary to increase the negative-sequence virtual admittance to improve the compensation effect.

[0071] It is understandable that when the negative sequence voltage increases, the negative sequence current increases, or the short-circuit ratio of the transformer substation decreases, the negative sequence adaptive virtual admittance will automatically increase, thereby enhancing the negative sequence absorption capability and achieving accurate negative sequence compensation. Compared with the method using a fixed compensation coefficient in the prior art, the adaptive admittance compensation method of the present invention can automatically match different operating conditions, avoiding overcompensation or undercompensation.

[0072] S5, Second Harmonic Power Oscillation Suppression: During negative-sequence compensation, the interaction between negative-sequence voltage and negative-sequence current generates second-harmonic active power oscillations, which in turn cause DC bus voltage fluctuations, affecting the stable operation of the energy storage converter. To address this issue, this embodiment establishes a second-harmonic power observation and suppression loop to estimate the second-harmonic power component caused by negative-sequence compensation online and limit its amplitude. The specific steps are as follows: Instantaneous active power decomposition: The instantaneous active power of grid-type energy storage can be decomposed into DC component and second harmonic AC component:

[0073] in, This represents the DC active power component. and These are the cosine and sine components of the second harmonic active power, respectively. For the instantaneous active power of grid-type energy storage, Let t be the system's rated angular frequency, and t be the time variable.

[0074] Second harmonic power amplitude calculation: Through low-pass filtering and coordinate transformation, the cosine and sine components of the second harmonic active power are extracted, and the second harmonic power amplitude is calculated.

[0075] in, This represents the fluctuation amplitude of the active power at second harmonic.

[0076] Second harmonic suppression coefficient generation: based on the upper limit of allowable second harmonic power. Generate the second harmonic suppression coefficient:

[0077] in, This is the second harmonic power oscillation suppression coefficient. This is a function that takes the minimum value.

[0078] In this embodiment, the upper limit of the second harmonic power is... The selection of this value is based on the withstand voltage capability of the DC bus capacitor and the thermal stability of the energy storage converter. Excessive fluctuations in the second harmonic power will cause the DC bus voltage to fluctuate beyond the allowable range, while also increasing the converter's heat generation and affecting the system's lifespan.

[0079] Negative sequence compensation current command correction: The negative sequence compensation current command is proportionally corrected using a second harmonic suppression coefficient.

[0080] in, This is the negative sequence compensation current command after being corrected by second-harmonic oscillation suppression.

[0081] When the second harmonic power amplitude is less than the allowable upper limit, the suppression coefficient The negative sequence compensation current command is not corrected; when the second harmonic power amplitude exceeds the allowable upper limit, the suppression coefficient... The negative-sequence compensation current command is reduced proportionally, thereby limiting the amplitude of the second harmonic power oscillation. This suppression strategy can effectively suppress the second harmonic power oscillation without completely shutting down the negative-sequence compensation, balancing compensation effectiveness and system stability.

[0082] S6, Capacity Constraint Correction: The capacity of grid-connected energy storage converters is limited. To ensure that grid support capability is not affected, this embodiment adopts a grid-priority capacity coordination mechanism, prioritizing the capacity required for positive-sequence grid connection, and then utilizing the remaining capacity for negative-sequence compensation. The specific steps are as follows: Positive-sequence grid capacity occupancy calculation: Based on the positive-sequence active power and positive-sequence reactive power, calculate the capacity required for positive-sequence grid construction.

[0083] in, The converter capacity required for normal-sequence network operation.

[0084] Remaining capacity calculation: Based on the rated capacity of the energy storage converter and the occupancy of the positive sequence grid capacity, the remaining capacity is calculated as follows:

[0085] in, This refers to the remaining capacity of the converter that can be used for negative sequence compensation.

[0086] Negative sequence compensation capacity requirement calculation: Based on the corrected negative sequence compensation current command, calculate the required capacity for negative sequence compensation.

[0087] in, The converter capacity required to perform negative sequence compensation, These are the coefficients of a three-phase system. This represents the amplitude of the negative sequence compensation current.

[0088] Capacity Coordination and Limitation: when When this occurs, it indicates that the remaining capacity is sufficient to meet the negative sequence compensation requirements, and full negative sequence compensation is executed. The negative sequence compensation current command that can be executed is:

[0089] when If the remaining capacity is insufficient to meet the negative sequence compensation requirement, the negative sequence compensation current command will be limited and corrected according to the ratio of the remaining capacity to the compensation requirement capacity.

[0090] in, This is the final executable negative sequence compensation current command after capacity constraint correction.

[0091] This capacity coordination mechanism ensures that grid-based energy storage always prioritizes positive-sequence voltage build-up, frequency stabilization, and inertia support, preventing excessive negative-sequence compensation from consuming converter capacity and reducing grid support capabilities. This is crucial for system stability in weak grid operation and high-penetration scenarios of distributed renewable energy.

[0092] S7, Three-phase modulation command generation: The positive-sequence grid-connected voltage command and the negative-sequence compensation current command after capacity constraints are transformed into a three-phase stationary coordinate system, adjusted by independent voltage and current controllers, and then superimposed to generate a three-phase modulation command. The specific steps are as follows: Inverse coordinate transformation: The positive-sequence grid voltage command and the negative-sequence compensation current command are respectively inversely transformed from the dq coordinate system to the three-phase stationary abc coordinate system:

[0093]

[0094] in, This is the inverse transformation matrix of Park. Adjustment for the Park inverse transform matrix controller, Positive sequence voltage control command in a three-phase stationary coordinate system. This is a negative sequence current control command in a three-phase stationary coordinate system. This is the Park inverse transformation matrix, which converts the dq rotating coordinate system components into three-phase stationary coordinate system components: Controller adjustment: Positive sequence voltage control: The positive sequence voltage deviation is adjusted by the grid voltage controller to generate the positive sequence voltage control quantity.

[0095] Negative sequence current control: The negative sequence current deviation is adjusted by a negative sequence current controller to generate a negative sequence current control quantity.

[0096] in, This is the voltage control quantity output by the positive sequence voltage controller. The control transfer function for the grid voltage controller is described in this embodiment, which uses a PI controller. The measured three-phase voltage at the grid connection point. This is the current control quantity output by the negative sequence current controller. This is the control transfer function for the negative sequence current controller. In this embodiment, a PI controller is used. The measured value of the three-phase negative sequence current at the grid connection point.

[0097] In this embodiment, both the grid voltage controller and the negative sequence current controller employ PI controllers. The parameters of the PI controllers are designed using frequency domain analysis to ensure the system has good dynamic response and steady-state accuracy. The proportional gain of the grid voltage controller is... The integral coefficient is The proportional gain of the negative sequence current controller is The integral coefficient is .

[0098] Synthesized three-phase modulation command: The positive-sequence voltage control quantity and the negative-sequence current control quantity are superimposed to obtain the final three-phase modulation command:

[0099] in, The final generated three-phase modulation wave command is used for subsequent SVPWM modulation. SVPWM modulation: Using Space Vector Pulse Width Modulation (SVPWM) technology, the three-phase modulation command is converted into switching drive signals for the converter's IGBTs. SVPWM modulation has advantages such as high DC voltage utilization and low harmonic content, which can effectively improve the converter's operating efficiency and power quality.

[0100] S8, converter execution: The grid-connected energy storage converter controls the on / off state of the IGBTs based on the switching drive signal generated by SVPWM modulation, outputting compensation voltage and current to achieve three-phase imbalance compensation at the grid connection point. The converter output, after being filtered by a filter inductor and capacitor, is injected into the grid connection point to counteract the negative sequence current generated by the load, thereby balancing the three-phase voltage and current.

[0101] During converter operation, it is necessary to monitor the converter's operating status in real time, including IGBT junction temperature, DC bus voltage, and output current. When faults such as overcurrent, overvoltage, or overheating occur, the converter will immediately enter protection mode and stop output to ensure the safety of equipment and personnel.

[0102] S9, feedback correction: To maintain a consistently effective three-phase imbalance compensation, this embodiment establishes a closed-loop feedback correction mechanism, adjusting control parameters online based on the compensated operating state. The specific steps are as follows: Compensation effect index calculation: Real-time calculation of voltage imbalance, current imbalance, and second harmonic power fluctuation after compensation.

[0103]

[0104] in, For voltage imbalance, This represents the degree of current imbalance.

[0105] Parameter adaptive adjustment: based on voltage imbalance Current imbalance and second harmonic power amplitude As a feedback mechanism, the negative-order virtual admittance coefficient is adjusted online every 100ms. , , and the upper limit of double frequency power .

[0106] The specific adjustment rules are as follows: when or If the compensation effect is insufficient, the negative-order virtual admittance coefficient should be appropriately increased. , , ; when If the second harmonic power oscillation is too large, the upper limit of the allowable second harmonic power should be appropriately reduced. ; when and and If the compensation effect is good and the system is stable, the negative sequence virtual admittance coefficient can be appropriately reduced to reduce the converter loss.

[0107] Through this closed-loop feedback correction mechanism, the system can automatically optimize control parameters based on the dynamic changes in the load of the distribution area and the grid conditions, and continuously maintain the best compensation effect.

[0108] To verify the effectiveness of the method described in this invention, experimental verification was conducted on the aforementioned 100kVA grid-type energy storage system experimental platform. The experimental conditions are as follows: Rated capacity of the transformer substation: 100kVA Short-circuit ratio of transformer substation: SCR=3 (weak network condition) Initial three-phase imbalance: voltage imbalance Current imbalance

[0109] Grid-type energy storage rated capacity: 100kVA DC bus voltage: 750V Rated voltage of the transformer substation: 380V / 50Hz During the experiment, data such as three-phase voltage, three-phase current, DC bus voltage, and second-harmonic power fluctuation at the grid connection point were recorded before and after compensation. The experimental results are as follows: Voltage imbalance: 15% before compensation, stabilized at 1.8% after compensation, meeting the requirement of no more than 2% voltage imbalance at the point of common coupling as specified in the standard "Power Quality Three-Phase Voltage Imbalance" (GB / T15543-2008). Current imbalance: 18% before compensation, stabilized at 2.1% after compensation, effectively balancing the three-phase load current. Second harmonic power fluctuation: 8.5kW before compensation, stabilized at 2.8kW after compensation, showing a significant suppression effect. DC bus voltage fluctuation: ±15V before compensation, ±4V after compensation, with a significant reduction in fluctuation amplitude. System frequency fluctuation: System frequency fluctuations before and after compensation were both less than ±0.1Hz, indicating that the inertia support capability of the grid-type energy storage was not affected by negative sequence compensation.

[0110] Experimental results show that the three-phase imbalance compensation method for grid-type energy storage with positive and negative sequence decoupling described in this invention can effectively address the three-phase imbalance problem in the transformer area while prioritizing grid support capabilities. It also suppresses second-harmonic power oscillations and DC bus voltage fluctuations, ensuring stable and reliable system operation.

[0111] This embodiment details a specific implementation method and system for decoupled positive and negative sequence three-phase imbalance compensation in grid-based energy storage. This invention solves the technical problem of coupling between negative sequence compensation and the main grid loop in existing technologies by constructing a dual-control channel architecture that completely decouples positive sequence grid construction and negative sequence compensation. It employs a positive and negative sequence separation method based on grid angle, eliminating the need for an external phase-locked loop and adapting to weak grid operating environments. A negative sequence adaptive virtual admittance compensation model is proposed, capable of adjusting compensation parameters online according to the degree of imbalance and grid strength, improving compensation accuracy. A second-harmonic power oscillation suppression loop is introduced to effectively suppress power oscillations and DC bus voltage fluctuations caused by negative sequence compensation. A grid-priority capacity coordination mechanism is adopted to ensure that grid support capacity is not affected.

[0112] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage, characterized in that, The method includes the following steps: S1 collects the three-phase voltage, three-phase current, DC bus voltage, energy storage state of charge, positive sequence active power, positive sequence reactive power, rated capacity of energy storage converter, and short-circuit ratio of the distribution area at the grid-connected point of the grid-type energy storage. S2, based on the positive sequence grid angle of grid-type energy storage, adopts a dual synchronous rotating coordinate system positive and negative sequence separation algorithm to extract the positive sequence voltage component and negative sequence voltage component at the grid connection point; S3, establish a positive sequence grid-building maintenance control channel based on the positive sequence voltage component, and generate a positive sequence grid-building voltage command; S4, establish a negative sequence adaptive admittance compensation channel based on the negative sequence voltage component, and generate a negative sequence compensation current command; S5, extract the second harmonic power component from the instantaneous active power of the grid-type energy storage, and perform oscillation suppression correction on the negative sequence compensation current command based on the amplitude of the second harmonic power; S6, calculate the remaining capacity based on the rated capacity of the energy storage converter and the positive sequence grid capacity occupancy, and perform capacity constraint correction on the negative sequence compensation current command based on the remaining capacity; S7 transforms the positive-sequence grid voltage command and the negative-sequence compensation current command after capacity constraint to the three-phase stationary coordinate system to generate a three-phase modulation command. S8 executes three-phase modulation commands through a grid-type energy storage converter to achieve three-phase imbalance compensation; S9 calculates the compensated voltage imbalance, current imbalance, and second harmonic power fluctuation in real time, and adaptively corrects the negative sequence virtual admittance parameter and second harmonic suppression coefficient based on the feedback results.

2. The method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage according to claim 1, characterized in that, In step S2, the three-phase voltage and current are first transformed by Clarke to obtain the components in the stationary coordinate system, and then transformed to the positive-sequence synchronous rotating coordinate system and the negative-sequence synchronous rotating coordinate system based on the positive-sequence grid angle, respectively. The transformed components are then low-pass filtered to obtain the positive-sequence voltage component and the negative-sequence voltage component, and a double-frequency cross decoupling stage is used to suppress the coupling disturbance between the positive and negative sequences.

3. The method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage according to claim 1, characterized in that, In step S3, the positive sequence grid-keeping control channel achieves active-frequency regulation through virtual inertia and virtual damping, maintains system frequency stability and provides inertia support, and generates positive sequence grid voltage amplitude through reactive-voltage coordinated regulation, and obtains the final positive sequence grid voltage command by combining the positive sequence grid angle.

4. The method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage according to claim 1, characterized in that, In step S4, the negative sequence compensation current command is generated by superimposing three parts: The first part is based on the generation of the product of negative-sequence adaptive virtual admittance and negative-sequence voltage; The second part is based on the generation of the proportional suppression term of the negative sequence current; The third part is the generation of dynamic damping terms based on negative sequence current.

5. The method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage according to claim 4, characterized in that, The negative-sequence adaptive virtual admittance is based on the basic negative-sequence admittance. It is adjusted online according to the ratio of negative-sequence voltage to positive-sequence voltage, the ratio of negative-sequence current to positive-sequence current, and the short-circuit ratio of the transformer area. When the negative-sequence voltage increases, the negative-sequence current increases, or the short-circuit ratio of the transformer area decreases, the negative-sequence adaptive virtual admittance automatically increases.

6. The method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage according to claim 1, characterized in that, In step S5, the instantaneous active power of the grid-type energy storage is decomposed into a DC component and a second harmonic AC component. The amplitude of the second harmonic AC component is calculated. A second harmonic suppression coefficient is generated based on the upper limit of the second harmonic power. The negative sequence compensation current command is proportionally corrected by the second harmonic suppression coefficient to limit the amplitude of the second harmonic power oscillation.

7. The method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage according to claim 1, characterized in that, In step S6, the positive sequence grid capacity occupancy is first calculated based on the positive sequence active power and positive sequence reactive power, and then the remaining capacity is calculated in combination with the rated capacity of the energy storage converter. When the capacity required for negative order compensation is less than or equal to the remaining capacity, perform full negative order compensation. When the required capacity for negative sequence compensation is greater than the remaining capacity, the negative sequence compensation current command is limited and corrected according to the ratio of the remaining capacity to the required compensation capacity.

8. The method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage according to claim 1, characterized in that, In step S7, the positive-sequence grid voltage command and the negative-sequence compensation current command after capacity constraint are first inversely transformed to the three-phase stationary coordinate system. Then, the positive-sequence voltage deviation is adjusted by the grid voltage controller, and the negative-sequence current deviation is adjusted by the negative-sequence current controller. The outputs of the two controllers are superimposed to obtain the three-phase modulation command.

9. The method for decoupling positive and negative sequence three-phase imbalance compensation in grid-type energy storage according to claim 1, characterized in that, In step S9, the voltage imbalance is the ratio of the negative sequence voltage amplitude to the positive sequence voltage amplitude, and the current imbalance is the ratio of the negative sequence current amplitude to the positive sequence current amplitude. Using voltage imbalance, current imbalance, and second harmonic power amplitude as feedback quantities, the correction coefficients of the negative sequence virtual admittance and the upper limit of the second harmonic power are adjusted online.

10. A grid-type energy storage positive and negative sequence decoupled three-phase imbalance compensation system, applicable to the grid-type energy storage positive and negative sequence decoupled three-phase imbalance compensation method according to any one of claims 1-9, characterized in that, The system consists of: The data acquisition module is used to collect three-phase voltage, three-phase current, DC bus voltage, energy storage state of charge, converter capacity, and transformer area short-circuit ratio at the grid connection point. The positive and negative sequence separation module is used to extract the positive and negative sequence voltage components based on the positive sequence grid angle of the grid-type energy storage. The positive sequence grid-building maintenance module is used to generate positive sequence grid-building voltage commands to achieve voltage build-up, frequency stabilization, and inertia support. The negative sequence adaptive admittance compensation module is used to generate negative sequence compensation current commands based on negative sequence voltage, negative sequence current and transformer area short-circuit ratio; The second harmonic power observation and suppression module is used to extract the second harmonic power component from the instantaneous active power and correct the negative sequence compensation current command according to the second harmonic power amplitude. The capacity coordination module is used to generate executable negative-sequence compensation current commands based on the positive-sequence grid capacity occupancy and the rated capacity of the energy storage converter. The modulation instruction generation module is used to combine the positive-sequence grid voltage instruction and the executable negative-sequence compensation current instruction into a three-phase modulation instruction; The converter execution module is used to drive the grid-type energy storage converter to output compensation voltage and compensation current; The feedback correction module is used to adaptively correct the negative sequence virtual admittance parameter and the second harmonic suppression coefficient based on the compensated voltage imbalance, current imbalance and second harmonic power fluctuation.

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