Grid-forming high-voltage direct-connected battery energy storage system and method

Abstract

The present invention provides a network-forming high-voltage directly-connected battery energy storage system and method, which relates to the technical field of electrical automation equipment and includes: a high-voltage directly-connected battery energy storage system, a network-forming control module, an internal potential power angle limiting module, and an internal potential amplitude limiting module; the high-voltage directly-connected battery energy storage system is used to disperse the battery modules in the system and connect them to the DC buses of each H-bridge circuit. The H-bridge circuits are cascaded on the AC side and then connected to the medium- and high-voltage power grid through filter inductors; the network-forming control module generates internal potential power angle and internal potential amplitude information by simulating the characteristics of a synchronous machine; the internal potential power angle limiting module and the internal potential amplitude limiting module are respectively used to calculate the limit values of the internal potential power angle and the internal potential amplitude in real time; the limited internal potential power angle and internal potential amplitude generate modulation signals for the high-voltage directly-connected battery energy storage system. The present invention can achieve current limitation and transient stability improvement during the transient faults of the high-voltage directly-connected battery energy storage system.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical automation equipment. Specifically, it relates to a grid-forming control and current-limiting control method for a high-voltage direct-connected battery energy storage system that can achieve single-inductor filtering without a current inner loop, and particularly to a grid-forming high-voltage direct-connected battery energy storage system and method. Background Art

[0002] Conventional battery energy storage system solutions are limited by technologies such as battery safety, battery grouping methods, and battery management systems. The single-unit capacity generally does not exceed 0.5 MW. Multiple such battery energy storage systems are paralleled to form a larger-capacity energy storage power station, and finally, they are connected to the medium-voltage and high-voltage power grids through step-up transformers in stages. In the energy storage power station based on the conventional battery energy storage system architecture, there are disadvantages such as large inter-cluster circulating currents in the battery stack, obvious cask effect, low battery utilization rate, and easy occurrence of safety problems. In addition, the parallel connection of multiple energy storage converters will result in a complex structure of the energy storage power station, a large floor area, a long cable line leading to complex distributed parasitic parameters, a slow system response time due to communication delay, a complex control system for the entire power station, and difficult coordinated control, making it difficult to meet the requirements for building 100 MW-class and GW-class energy storage power stations in the future.

[0003] The high-voltage direct-connected battery energy storage system based on the cascaded H-bridge converter has a highly modular structure, which is convenient for capacity expansion and redundant design, and can eliminate the loss caused by the power frequency transformer by directly connecting to the high-voltage power grid. The large-capacity battery stack is dispersed and connected to each H-bridge circuit with a single battery cluster as a unit, avoiding the circulating current in the battery stack, reducing the system cycle loss, and improving the system safety at the same time. Compared with the traditional energy storage system, the high-voltage direct-connected battery energy storage system realizes a large single-unit capacity. When forming a large-scale energy storage power station, the number of parallel units required is small, reducing the floor area of the power station. The power station structure and control strategy are simple, the system response speed is fast, and it is not easy to cause system stability problems, which can meet the requirements for building a large-capacity battery energy storage power station.

[0004] The high-voltage direct-connected battery energy storage system combines the fast response speed of the power electronic converter to achieve the inherent synchronization characteristics of the synchronous machine, that is, grid-forming control, by simulating the operating characteristics of a reference synchronous machine, thereby providing active support for the power grid in terms of active and reactive power. The high-voltage direct-connected battery energy storage system combines the advantages of the power electronic converter and the battery energy storage system to construct a large-capacity static synchronous machine with the performance of a synchronous machine or even exceeding that of a traditional synchronous generator, which is of great significance for building a new power system with new energy as the main body. The modular multi-level topology characteristics of the high-voltage direct-connected battery energy storage system make the current harmonics small after being connected to the grid through the grid-side filter inductor. At the same time, the cost of capacitors in the high-voltage system is high and the reliability is low. Therefore, there is no capacitive filtering at the grid connection point in the high-voltage direct-connected battery energy storage system topology.

[0005] However, in the grid-forming control of traditional low-voltage systems, due to the presence of filter inductors and filter capacitors on the grid side, the voltage control of the grid connection point is achieved through the double-loop control of the outer-loop voltage and the inner-loop current. This double-loop control structure based on it cannot be directly applied to the grid-forming control of high-voltage directly-connected battery energy storage systems. The characteristic of no AC filter capacitor also makes it difficult to construct the grid connection point voltage, which further deteriorates the grid-forming control performance and makes it difficult to set the control parameters. It will also cause problems such as active-reactive power coupling, large island voltage harmonics, and oscillation instability. Therefore, it is necessary to study the grid-forming control strategy applicable to high-voltage directly-connected battery energy storage systems.

[0006] In the prior art, the following grid-forming control methods have been proposed:

[0007] The invention patent with the publication number CN117674228A discloses a grid-forming energy storage system, analyzes the causes of current operation faults of the energy storage system, and records the support information of power emergency events and the operation state of the battery at the moment of emergency support time. From the aspects of grid-forming energy storage configuration and operation strategy, it solves the problem of ensuring the stability of the power system when the electric energy changes. The patent also points out the problems that need to be solved in the control of the grid-forming energy storage system.

[0008] The invention patent with the publication number CN119070363A discloses a grid-forming high-voltage directly-connected battery energy storage system and method. This invention relies on the current inner loop control to limit the transient current. The current inner loop is prone to stability risks under weak grids, and after the grid fault triggers the current limit, the external characteristics of the energy storage system are affected by the current limit and are prone to synchronous stability problems.

[0009] In summary, the technical problems in the prior art are as follows: In the existing grid-forming control architecture, the current inner loop is relied on to limit the transient current during faults, and the current inner loop is prone to stability risks under steady state and instability risks under transient state. Summary of the Invention

[0010] In view of the defects in the prior art, the present invention provides a grid-forming high-voltage directly-connected battery energy storage system and method.

[0011] According to a grid-forming high-voltage directly-connected battery energy storage system and method provided by the present invention, the solution is as follows:

[0012] In the first aspect, a grid-forming high-voltage directly-connected battery energy storage system is provided. The system includes: a high-voltage directly-connected battery energy storage system, a grid-forming control module, an internal potential power angle limitation module, and an internal potential amplitude limitation module;

[0013] The high-voltage direct-connected battery energy storage system is used to connect the battery modules in the system to the DC buses of each H-bridge circuit in a decentralized manner. The H-bridge circuits are cascaded on the AC side and then connected to the medium- and high-voltage power grid through filter inductors.

[0014] The grid-forming control module generates internal potential power angle and internal potential amplitude information by simulating the characteristics of a synchronous machine.

[0015] The internal potential power angle limiting module is used to calculate the limited amplitude value of the internal potential power angle generated by the grid-forming control module in real time.

[0016] The internal potential amplitude limiting module is used to calculate the limited amplitude value of the internal potential amplitude generated by the grid-forming control module in real time.

[0017] The limited internal potential power angle and internal potential amplitude are used to generate the modulation signal of the high-voltage direct-connected energy storage system, realizing current limitation and transient stability improvement during the transient fault of the high-voltage direct-connected battery energy storage system.

[0018] Preferably, the system further includes: a virtual impedance module;

[0019] The virtual impedance module is used to simulate the virtual impedance characteristics between the internal potential and the grid connection point, enhancing the system's ability to operate with a wide short-circuit ratio.

[0020] Preferably, the limited internal potential power angle and internal potential amplitude output by the internal potential power angle limiting module and the internal potential amplitude limiting module are used to generate a voltage in the stationary coordinate system, and then subtract the product of the grid-connected current and the virtual impedance to generate the modulation signal of the high-voltage direct-connected energy storage.

[0021] Preferably, the maximum value θ max and the minimum value θ min of the power angle calculated in the internal potential power angle limiting module are:

[0022]

[0023] where, v d is the actual value of the grid connection point d-axis voltage, v q is the actual value of the grid connection point q-axis voltage, is the amplitude of the impedance between the internal potential and the grid connection point, which is the sum of the virtual impedance and the filter impedance, R v is the virtual resistance, is the inductive reactance of the virtual inductor, R f is the filter resistance, is the inductive reactance of the filter inductor, Imax is the current limit amplitude value, V PCC is the amplitude of the grid connection point voltage, θ is the power angle calculated by the internal potential power angle limit module;

[0024] The maximum and minimum limit amplitude values of the power angle calculated by the internal potential power angle limit module are used to limit the magnitude of the power angle output by the grid-forming control module.

[0025] Preferably, the maximum value of the internal potential calculated in the internal potential amplitude limit module E max and the minimum value E min are:

[0026]

[0027] The maximum and minimum limit amplitude values of the amplitude calculated by the internal potential amplitude limit module are used to limit the magnitude of the internal potential amplitude output by the grid-forming control module.

[0028] In a second aspect, a grid-forming type high-voltage direct-connected battery energy storage method is provided, and the method includes:

[0029] Step S1: The grid-forming control module outputs the internal potential power angle of the high-voltage direct-connected battery energy storage system through the primary frequency modulation link, the virtual inertia link and the damping control link; outputs the internal potential amplitude of the high-voltage direct-connected battery energy storage system through the reactive power-voltage droop link and the internal potential regulation link;

[0030] Step S2: Through the internal potential power angle limit module and the internal potential amplitude limit module, calculate the maximum and minimum values of the power angle and the amplitude respectively, and perform amplitude limiting control on the internal potential power angle and the internal potential amplitude generated in Step S1 respectively to obtain the amplitude-limited internal potential power angle and internal potential amplitude;

[0031] Step S3: Output the modulation command before amplitude limiting of the high-voltage direct-connected battery energy storage system through the virtual impedance module;

[0032] The high-voltage direct-connected battery energy storage system dispersedly connects the battery modules to the DC buses of each H-bridge circuit. The H-bridge circuits are cascaded on the AC side and then connected to the medium-voltage and high-voltage power grid through the filter inductors.

[0033] Preferably, the virtual impedance module in Step S3 simulates the virtual impedance characteristics between the internal potential and the grid connection point to enhance the system's ability to operate with a wide short-circuit ratio.

[0034] Preferably, the limited internal potential angle and the limited internal potential amplitude output by the internal potential angle limitation module and the internal potential amplitude limitation module in the step S2 are used to generate a voltage in the stationary coordinate system, and then subtract the product of the grid-connected current and the virtual impedance to generate the modulation signal of the high-voltage direct-connected energy storage.

[0035] Preferably, in the step S2, calculate the maximum value of the power angle θ max and the minimum value θ min as:

[0036]

[0037] wherein, v d is the actual value of the grid connection point d-axis voltage, v q is the actual value of the grid connection point q-axis voltage, is the amplitude of the impedance between the internal potential and the grid connection point, which is the sum of the virtual impedance and the filter impedance, R v is the virtual resistance, is the inductive reactance of the virtual inductor, R f is the filter resistance, is the inductive reactance of the filter inductor, I max is the current limit value, V PCC is the amplitude of the grid connection point voltage, θ is the power angle calculated by the internal potential angle limitation module;

[0038] The maximum and minimum limit values of the power angle calculated by the internal potential angle limitation module are used to limit the magnitude of the power angle output by the network-forming control module.

[0039] Preferably, in the step S2, calculate the maximum value of the internal potential E max and the minimum value E min as:

[0040]

[0041] The maximum and minimum limit values of the amplitude calculated by the internal potential amplitude limitation module are used to limit the magnitude of the internal potential amplitude output by the network-forming control module.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The internal potential power angle limiting module in the present invention realizes the rapid change of the internal potential power angle of the network-forming energy storage, improving the stability of the system in grid voltage and phase angle jump faults. The internal potential amplitude limiting module accurately limits the transient current amplitude and at the same time improves the support performance for the power grid. By directly limiting the power angle and phase of the internal potential, the current inner loop control link is cancelled in the control loop, which can not only accurately limit the transient current but also improve the transient stability ability during grid faults.

[0044] 2. The present invention also designs a virtual impedance link, which can achieve stable operation under a wide short-circuit ratio of the power grid.

[0045] 3. The present invention can achieve the network-forming control of a multi-level topology with single-inductor filtering such as a high-voltage direct-connected battery energy storage system, and can still achieve the network-forming control and fault current limiting ability of the high-voltage direct-connected battery energy storage system without relying on the existence of an AC-side filtering capacitor.

[0046] 4. The present invention realizes that the high-voltage direct-connected battery energy storage system exhibits voltage source characteristics. The proposed internal potential power angle limitation and amplitude limitation can directly limit the amplitude and phase information of the internal potential, and can achieve precise control of the transient fault current without relying on the inner loop closed-loop control, improving the AC voltage control performance of the network-forming high-voltage direct-connected battery energy storage system, enabling it to synchronize with the power grid autonomously and operate stably, having autonomous inertia response and primary frequency modulation capabilities, providing short-circuit current support during grid faults, having the stable network-forming operation ability to connect to the grid with load and transfer to island mode, being able to establish voltage autonomously, having the black start function, achieving zero-start voltage boost and supplying power to the outside.

[0047] Other beneficial effects of the present invention will be described through the introduction of specific technical features and technical solutions in the specific implementation manner. Those skilled in the art should be able to understand the beneficial technical effects brought by the described technical features and technical solutions through these introductions. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Other features, objectives and advantages of the present invention will become more obvious by reading the detailed description of the non-limiting embodiments with reference to the following drawings:

[0049] Figure 1 is the control block diagram of the network-forming high-voltage direct-connected battery energy storage system;

[0050] Figure 2 is the control block diagram of the active power frequency control module of the network-forming high-voltage direct-connected battery energy storage system;

[0051] Figures 3a - 3b respectively represent the low-voltage fault simulation waveforms under high short-circuit ratio and the low-voltage fault simulation waveforms under low short-circuit ratio. DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all belong to the protection scope of the present invention.

[0053] An embodiment of the present invention provides a grid-forming high-voltage direct-connected battery energy storage system. The proposed no-current internal grid-forming control, internal potential power angle limit and amplitude limit control improve the AC voltage control performance of the grid-forming high-voltage direct-connected battery energy storage system. Precise control of the fault current is achieved under the no-current inner loop, enabling it to autonomously synchronize with the grid and operate stably, having autonomous inertia response and primary frequency regulation capabilities. It can provide short-circuit current support during grid faults, has the stable grid-forming operation ability to connect to the grid with load and transfer to islanding, can autonomously establish voltage, has a black start function, realizes zero-start voltage boost and supplies power externally.

[0054] Referring to Figure 1 as shown, the Figure 1 in which, L g represents the grid impedance, L f represents the filter reactance, R f represents the filter resistance, BM represents the energy storage sub-module, v mabc represents the modulation voltage, abc represents phase A, phase B, and phase C, dq represents the d-axis and q-axis in the rotating coordinate system, v represents the grid connection point voltage, i represents the grid connection point current, P represents the active power output of the system, Q represents the reactive power output of the system, V represents the grid connection point voltage amplitude, V PCC is the grid connection point voltage amplitude, V ref represents the voltage set value, Q ref represents the reactive power reference value, D q represents the reactive voltage droop coefficient, K represents the reactive loop integral coefficient, s represents the differential operator, E max represents the maximum value of the internal potential limit, E min represents the minimum value of the internal potential limit, E represents the internal potential amplitude, V md represents the d-axis modulation voltage, V mq represents the q-axis modulation voltage R v is the virtual resistance, represents the inductive reactance of the virtual inductor, i d represents the d-axis current, iq represents the q-axis current, P ref represents the actual active power reference value, J represents the virtual inertia coefficient, ω represents the AC angular frequency, ω n represents the rated angular frequency, represents the angular frequency difference, D p represents the primary frequency regulation droop coefficient, θ max represents the maximum value of the power angle, θ min represents the minimum value of the power angle.

[0055] Specifically, the system includes: a high-voltage direct-connected battery energy storage system, a grid-forming control module, a virtual impedance module, an internal potential power angle limitation module, and an internal potential amplitude limitation module.

[0056] The high-voltage direct-connected battery energy storage system is used to disperse the battery modules in the system and connect them to the DC buses of each H-bridge circuit. The H-bridge circuits are cascaded on the AC side and then connected to the medium- and high-voltage power grid through filter inductors.

[0057] The grid-forming control module generates the power angle and amplitude information of the internal potential by simulating the characteristics of a synchronous machine; the grid-forming control module includes an active frequency control module and a reactive voltage control module;

[0058] Among them, the active frequency control module realizes the virtual inertia and primary frequency regulation functions through the power synchronization method, can achieve synchronization with the power grid independently without a phase-locked loop, and has the ability of autonomous frequency regulation. The reactive voltage control module has the ability of autonomous voltage regulation by realizing that the reactive power and voltage satisfy the droop characteristics.

[0059] The virtual impedance module enhances the operation ability of the system with a wide short-circuit ratio by simulating the virtual impedance characteristics between the internal potential and the grid connection point.

[0060] The internal potential power angle limitation module and the amplitude limitation module are used to calculate the limited amplitude values of the power angle generated by the active frequency control module in the grid-forming control module in real time, and calculate the limited amplitude values of the internal potential amplitude generated by the reactive voltage control module in the grid-forming control module. The limited internal potential power angle and internal potential amplitude are used to generate the modulation signal of the high-voltage direct-connected energy storage system, realizing current limitation and transient stability improvement during the transient fault of the high-voltage direct-connected battery energy storage system. Specifically, the limited internal potential power angle and internal potential amplitude output by the internal potential power angle limitation module and the internal potential amplitude limitation module are used to generate the voltage in the stationary coordinate system, and then subtract the product of the grid-connected current and the virtual impedance to generate the modulation signal of the high-voltage direct-connected energy storage.

[0061] Specifically, the maximum value of the power angle is calculated in the internal potential power angle limitation module θ max and the minimum value θ min are:

[0062]

[0063] Among them, v d is the actual value of the d-axis voltage at the grid connection point, v q is the actual value of the q-axis voltage at the grid connection point, is the magnitude of the impedance between the internal potential and the grid connection point, which is the sum of the virtual impedance and the filter impedance, R v is the virtual resistance, is the reactance of the virtual inductor, R f is the filter resistance, is the reactance of the filter inductor, I max is the current limit value, V PCC is the magnitude of the grid connection point voltage, θ is the power angle calculated by the internal potential power angle limitation module;

[0064] The maximum and minimum limit values of the power angle calculated by the internal potential power angle limitation module are used to limit the magnitude of the power angle output by the active power frequency control module.

[0065] In the internal potential magnitude limitation module, the maximum value of the internal potential is calculated E max and the minimum value E min are:

[0066]

[0067] The maximum and minimum limit values of the magnitude calculated by the internal potential magnitude limitation module are used to limit the magnitude of the internal potential output by the reactive voltage control module.

[0068] Referring to Figure 2 shown, the active power frequency control module generates the command value of the active power through the primary frequency modulation link:

[0069]

[0070] Among them, ω n is the rated angular frequency, ω g is the grid angular frequency, D p is the primary frequency modulation droop coefficient,P set is the set value of the active power at the grid connection point, P ref is the reference value of the actual active power, P max is the maximum active power of the high-voltage direct-connected battery energy storage system, Figure 2 P in s represents the actual power feedback value;

[0071] Then, the power angle of the high-voltage direct-connected battery energy storage system is output through the virtual inertia link and the damping control link:

[0072]

[0073] Among them, J is the virtual inertia coefficient, s is the differential operator, D d is the damping coefficient, P PCC is the actual value of the active power at the grid connection point.

[0074] The reactive power and voltage control module outputs the amplitude of the internal potential through the reactive power and voltage droop link and the internal potential regulation link:

[0075]

[0076] Among them, E is the amplitude of the internal potential, ω n is the rated angular frequency, K is the internal potential regulation coefficient, s is the differential operator, D q is the reactive power and voltage droop coefficient, V N is the rated value of the grid-connected voltage, V PCC is the amplitude of the grid-connected voltage, Q set is the set value of the reactive power at the grid connection point, Q PCC is the actual value of the reactive power at the grid connection point.

[0077] Referring to Figures 3a - 3b shown, are the simulation waveforms of the grid low-voltage fault occurring under two different grid strengths with the proposed grid-forming control. The accurate control of the fault current is achieved at the rated 1.2 pu without current inner loop, and instability does not occur while providing voltage support.

[0078] The present invention also provides a grid-forming high-voltage direct-connected battery energy storage method, which specifically includes:

[0079] Step S1: The active power frequency control module in the network-forming control module outputs the power angle of the network-forming type high-voltage directly-connected battery energy storage system through the primary frequency modulation link, the virtual inertia link, and the damping control link; the reactive power voltage control module in the network-forming control module outputs the amplitude of the internal electromotive force of the high-voltage directly-connected battery energy storage system through the reactive power voltage droop link and the internal electromotive force regulation link.

[0080] Step S2: Through the internal electromotive force power angle limit module and the internal electromotive force amplitude limit module, calculate the maximum and minimum values of the power angle and amplitude respectively, and perform amplitude limit control on the internal electromotive force power angle and amplitude generated in Step S1 to obtain the new internal electromotive force power angle and amplitude; specifically as follows:

[0081] The internal electromotive force power angle limit module calculates the maximum value of the power angle θ max and the minimum value θ min as:

[0082]

[0083] where v d is the actual value of the grid connection point d-axis voltage, v q is the actual value of the grid connection point q-axis voltage, is the amplitude of the impedance between the internal electromotive force and the grid connection point, which is the sum of the virtual impedance and the filter impedance, R v is the virtual resistance, is the inductive reactance of the virtual inductor, R f is the filter resistance, is the inductive reactance of the filter inductor, I max is the current limit value, V PCC is the amplitude of the grid connection point voltage, θ is the power angle calculated by the internal electromotive force power angle limit module.

[0084] The internal electromotive force amplitude limit module calculates the maximum value of the internal electromotive force E max and the minimum value E min as:

[0085]

[0086] Step S3: The virtual impedance module outputs the modulation command before amplitude limiting of the high-voltage directly-connected battery energy storage system by simulating the virtual impedance characteristics between the internal potential and the grid connection point; the amplitude-limited internal potential power angle and internal potential amplitude output by the internal potential power angle limiting module and the internal potential amplitude limiting module are used to generate the voltage in the stationary coordinate system, and then subtract the product of the grid-connected current and the virtual impedance to generate the modulation signal of the high-voltage directly-connected energy storage.

[0087] The high-voltage directly-connected battery energy storage system dispersedly connects the battery modules to the DC buses of each H-bridge circuit. The H-bridge circuits are cascaded on the AC side and then connected to the medium- and high-voltage power grid through the filter inductance.

[0088] Specifically, referring to Figure 2 as shown, the active power frequency control module generates the command value of the active power through the primary frequency modulation link:

[0089]

[0090] where ω n is the rated angular frequency, ω g is the grid angular frequency, D p is the primary frequency modulation droop coefficient, P set is the grid connection point active power set value, P ref is the actual active power reference value, P max is the maximum active power of the high-voltage directly-connected battery energy storage system;

[0091] Then, the power angle of the high-voltage directly-connected battery energy storage system is output through the virtual inertia link and the damping control link:

[0092]

[0093] where J is the virtual inertia coefficient, s is the differential operator, D d is the damping coefficient, P PCC is the actual value of the grid connection point active power.

[0094] When the grid connection point voltage is lower than the low voltage fault judgment threshold V th_low , adjust the grid connection point active power set value to zero and multiply the grid connection point power feedback value P PCC by an amplification factor. By selecting an appropriate factor, the active power loop response characteristics and response time during the transient low voltage fault can be made basically consistent with the steady state.

[0095] Referring to Figures 3a - 3b As shown, the simulation waveforms of grid low voltage faults occurring under two different grid strengths under the proposed grid-forming control are presented. Precise control of the fault current is achieved at 1.2 pu of the rated value without a current inner loop, and instability does not occur while providing voltage support.

[0096] The embodiment of the present invention provides a grid-forming high-voltage direct-connected battery energy storage system and method. Through the proposed grid-forming control method of the high-voltage direct-connected battery energy storage system without a current inner loop, the high-voltage direct-connected battery energy storage system can exhibit voltage source characteristics during grid-connected and off-grid conditions. The proposed control of the internal potential power angle limit and amplitude limit can achieve precise control of the transient fault current by directly limiting the amplitude and phase information of the internal potential, and at the same time, the transient stability and support ability are improved.

[0097] Those skilled in the art know that in addition to implementing the system and its various devices, modules, and units provided by the present invention in the form of pure computer-readable program code, the method steps can be logically programmed to enable the system and its various devices, modules, and units provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers, etc., to achieve the same functions. Therefore, the system and its various devices, modules, and units provided by the present invention can be regarded as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be regarded as the structure within the hardware component; the devices, modules, and units for implementing various functions can also be regarded as either software modules for implementing the method or the structure within the hardware component.

[0098] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Without conflict, the embodiments of the present application and the features in the embodiments can be combined arbitrarily with each other.

Claims

1. A grid-forming high-voltage direct-connected battery energy storage system, characterized in that, Including: A high-voltage direct-connected battery energy storage system, a grid-forming control module, an internal potential power angle limiting module, and an internal potential amplitude limiting module; The high-voltage direct-connected battery energy storage system is used to disperse the battery modules in the system and connect them to the DC buses of each H-bridge circuit. The H-bridge circuits are cascaded on the AC side and then connected to the medium- and high-voltage power grid through filter inductors; The grid-forming control module generates internal potential power angle and internal potential amplitude information by simulating the characteristics of a synchronous machine; The internal potential power angle limiting module is used to calculate the limit amplitude of the internal potential power angle generated by the grid-forming control module in real time; The internal potential amplitude limiting module is used to calculate the limit amplitude of the internal potential amplitude generated by the grid-forming control module in real time; The limited internal potential power angle and internal potential amplitude are used to generate the modulation signal of the high-voltage direct-connected battery energy storage system, realizing current limitation and transient stability improvement during the transient fault of the high-voltage direct-connected battery energy storage system; Calculate the maximum value of the power angle in the internal potential power angle limiting module θ max and the minimum value θ min are as follows: Among them, v d is the actual value of the d-axis voltage at the grid connection point, v q is the actual value of the q-axis voltage at the grid connection point, is the magnitude of the impedance between the internal electromotive force and the grid connection point, which is the sum of the virtual impedance and the filter impedance, R v is the virtual resistance, is the inductive reactance of the virtual inductor, R f is the filter resistance, is the inductive reactance of the filter inductor, I max is the current limit value, V PCC is the magnitude of the grid connection point voltage, θ is the power angle calculated by the internal electromotive force power angle limit module; The maximum and minimum limit amplitudes of the power angle calculated by the internal potential power angle limiting module are used to limit the magnitude of the power angle output by the grid-forming control module.

2. The network-forming high-voltage direct-connected battery energy storage system according to claim 1, wherein The system further includes: a virtual impedance module; The virtual impedance module is used to simulate the virtual impedance characteristics between the internal potential and the grid connection point, enhancing the system's ability to operate with a wide short-circuit ratio.

3. The network-forming high-voltage direct-connected battery energy storage system according to claim 2, wherein The internal potential power angle limiting module and the internal potential amplitude limiting module output the limited internal potential power angle and internal potential amplitude, which are used to generate the voltage in the stationary coordinate system, and then subtract the product of the grid-connected current and the virtual impedance to generate the modulation signal of the high-voltage direct-connected energy storage.

4. The grid-forming high-voltage directly-connected battery energy storage system according to claim 1, wherein Calculate the maximum value of the internal potential in the internal potential amplitude limiting module E max and the minimum value E min are as follows: The maximum and minimum limit amplitudes of the amplitude calculated by the internal potential amplitude limiting module are used to limit the magnitude of the internal potential amplitude output by the grid-forming control module.

5. A grid-forming high-voltage direct-connected battery energy storage method, based on the grid-forming high-voltage direct-connected battery energy storage system according to any one of claims 1-4, characterized in that, Including: Step S1: The grid-forming control module outputs the internal potential power angle of the high-voltage direct-connected battery energy storage system through a primary frequency regulation link, a virtual inertia link, and a damping control link; outputs the internal potential amplitude of the high-voltage direct-connected battery energy storage system through a reactive power-voltage droop link and an internal potential regulation link; Step S2: Through the internal potential power angle limiting module and the internal potential amplitude limiting module, calculate the maximum and minimum values of the power angle and amplitude respectively, and perform limit control on the internal potential power angle and internal potential amplitude generated in Step S1 to obtain the limited internal potential power angle and internal potential amplitude; Step S3: Output the modulation command before limiting of the high-voltage direct-connected battery energy storage system through the virtual impedance module; The high-voltage direct-connected battery energy storage system disperses the battery modules and connects them to the DC buses of each H-bridge circuit. The H-bridge circuits are cascaded on the AC side and then connected to the medium- and high-voltage power grid through filter inductors.

6. The grid-forming high-voltage direct-connected battery energy storage method according to claim 5, wherein The virtual impedance module in Step S3 simulates the virtual impedance characteristics between the internal potential and the grid connection point, enhancing the system's ability to operate with a wide short-circuit ratio.

7. The grid-forming high-voltage direct-connected battery energy storage method according to claim 6, wherein The internal potential power angle limiting module and the internal potential amplitude limiting module in Step S2 output the limited internal potential power angle and internal potential amplitude, which are used to generate the voltage in the stationary coordinate system, and then subtract the product of the grid-connected current and the virtual impedance to generate the modulation signal of the high-voltage direct-connected energy storage.

8. The grid-forming high-voltage direct-connected battery energy storage method according to claim 5, wherein In the said step S2, calculate the maximum value of the power angle θ max and the minimum value θ min as follows: Wherein, v d is the actual value of the d-axis voltage at the grid connection point, v q is the actual value of the q-axis voltage at the grid connection point, is the magnitude of the impedance between the internal electromotive force and the grid connection point, which is the sum of the virtual impedance and the filter impedance, R v is the virtual resistance, is the inductive reactance of the virtual inductor, R f is the filter resistance, is the inductive reactance of the filter inductor, I max is the current limit value, V PCC is the magnitude of the grid connection point voltage, θ is the power angle calculated by the internal electromotive force power angle limit module; The maximum and minimum limit values of the power angle calculated by the internal potential power angle limitation module are used to limit the power angle magnitude output by the network-forming control module.

9. The grid-forming high-voltage direct-connected battery energy storage method according to claim 5, wherein In the step S2, calculate the maximum value of the internal electric potential E max and the minimum value E min as follows: The maximum and minimum limit values of the amplitude calculated by the internal potential amplitude limitation module are used to limit the internal potential amplitude magnitude output by the network-forming control module.

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