A multi-machine parallel grid energy storage converter fault ride-through method

Abstract

The application belongs to the technical field of energy storage systems, and relates to a multi-machine parallel network energy storage converter fault ride-through method. θ ref The internal potential E output by the reactive power ring is combined to obtain a modulation wave; during normal operation, the switch is connected to the 1 / s integral link, and the system frequency is stabilized in cooperation with the active power ring; when a fault occurs, the switch is disconnected and does not access any link, and the system operates at a fixed frequency; when the fault is recovered, the switch is connected to the k d The proportional link and the 1 / s integral link are connected in parallel branches, power and frequency oscillations are quickly suppressed, and the system gradually recovers to normal; the application can ensure that the multi-machine parallel energy storage converter system realizes frequency synchronization, power balance and stable output during the whole fault ride-through process, greatly improves the fault ride-through capability and grid connection adaptability of the system, and provides a reliable technical guarantee for stable operation of a large-scale energy storage substation.

Description

Technical Field

[0001] This invention belongs to the field of energy storage system technology, specifically relating to a fault ride-through method for a multi-machine parallel grid-connected energy storage converter. Background Technology

[0002] With the continuous increase in the penetration rate of new energy power generation, energy storage systems, with energy storage converters at their core, are playing an increasingly crucial role in voltage regulation, frequency regulation, and fault support in power systems. Energy storage converters, essentially power electronic devices, have drawbacks such as weak damping and low inertia, resulting in significant differences in electromechanical characteristics compared to traditional synchronous generators. This leads to problems such as frequency instability, power oscillation, and excessive current in multi-unit parallel energy storage converters during grid faults (such as voltage sags, dips, and short circuits) and fault recovery, seriously threatening the stable operation of the power system and limiting the fault ride-through capability of energy storage converters. To address these issues, virtual synchronous generator technology from grid control is employed. By introducing rotor oscillation equations to simulate the inertia and damping characteristics of traditional generators, the energy storage converter is endowed with "synchronous machine-like" external characteristics, improving its frequency anti-interference capability. Under external disturbances such as grid faults, the grid-connected converter exhibits voltage source characteristics, demonstrating stronger grid support capabilities. Multi-unit parallel energy storage converters have become the mainstream topology for large-scale energy storage substations due to their advantages such as flexible capacity expansion, high reliability, and redundancy.

[0003] However, most existing technologies focus on current limiting and fault ride-through strategies for single grid-connected converters connected to a large power grid, with less consideration given to the collaborative operation characteristics of multi-converter parallel grid systems. In existing virtual synchronous generator control strategies, the virtual inertia element often uses a single integral element (1 / s) to simulate the rotor's motion characteristics. During faults, the integral element of a multi-converter parallel system is prone to saturation. Power changes caused by grid faults are amplified through the integral element, exacerbating system frequency fluctuations and causing the converter output current to exceed limits. Traditional virtual damped power elements directly multiply the angular frequency deviation by the damping coefficient to obtain damped power, resulting in participation in power distribution in both steady-state and dynamic states. Since deviations in a multi-converter parallel system cannot be completely eliminated in steady state, the damped power persists, affecting the accuracy of active power distribution and reducing system operating efficiency.

[0004] Therefore, a method is needed to adapt to the fault ride-through of multi-machine parallel grid-connected energy storage converters in order to solve the above-mentioned technical problems. Summary of the Invention

[0005] This application aims to achieve virtual damping that exists dynamically but is zero in steady state by modifying the virtual damping power loop and virtual inertia loop. Furthermore, it adaptively switches branches according to different system operating conditions, achieving current limiting, power angle stabilization, and frequency synchronization control through simultaneous adjustment of the power loop and virtual impedance.

[0006] This invention provides the following technical solution: a fault ride-through method for multi-machine parallel grid-connected energy storage converters, which achieves frequency synchronization and current limiting of the multi-machine parallel system through an active power loop, and then generates an angle from the active power loop. i ref The modulated wave is obtained by combining the internal potential E output by the reactive power loop with the modulated wave, ensuring the stable operation of the multi-machine parallel energy storage converter system during fault ride-through.

[0007] During normal operation, the switches in the active power loop are connected to the 1 / s integral link, which works with the active power loop to stabilize the system frequency.

[0008] When a fault occurs, the switches in the active power loop are disconnected and not connected to any link, and the system operates at a fixed frequency.

[0009] During fault recovery, the switch in the active power loop is connected to k. d The proportional element and the 1 / s integral element are connected in parallel to quickly suppress power and frequency oscillations, allowing the system to gradually return to normal.

[0010] Preferably, the active power loop is implemented as follows: virtual mechanical power. P m With virtual electromagnetic power P e The difference Δ P With virtual damping power P damp After subtraction, the result is fed into the virtual inertia stage 1 / Yes s Virtual inertia element 1 / Yes s The switch selects the first 1 / s integral stage during normal operation, and the output... oh-oh s Enter k during fault recovery d The proportional element and the 1 / s integral element are connected in parallel in the branch, and the output of the 1 / s integral element is... oh-oh s ;in, oh-oh s After passing through a first-order inertial element 1 / (1+As), and then the damping coefficient D Multiply to form virtual damping power P damp ;at the same time, oh-oh s After the second 1 / s integral stage, and k d The output superposition yields the internal potential phase reference value. i ref .

[0011] The reactive power loop is implemented by referencing reactive power. Q refand actual reactive power Q After the difference is calculated, it passes through the proportional element k. Q And superimposed voltage amplification command E ref The internal potential E is obtained.

[0012] More preferably, during normal operation, the fault ride-through method uses the following equation to simulate the oscillation equation of the rotor of a traditional synchronous generator in the active power control loop of the virtual synchronous generator: (1) In equation (1), J For virtual rotational inertia, oh s To synchronize the reference angular frequency, oh For the angular frequency of the virtual synchronizer, t For time, P m For virtual mechanical power, P e For virtual electromagnetic power, P damp This represents the virtual damping power.

[0013] More preferably, in the fault-crossing method, during fault recovery, the switch is connected to k. d The branch with the proportional element and the 1 / s integral element connected in parallel is represented by the following formula: (2) In equation (2), J For virtual rotational inertia, oh s To synchronize the reference angular frequency, oh For the angular frequency of the virtual synchronizer, t For time, P m For virtual mechanical power, P e For virtual electromagnetic power, P damp For virtual damping power, k d This is the coefficient for the proportional element.

[0014] More preferably, in the active power loop, the virtual mechanical power P m Subtract virtual electromagnetic power P e The power deviation Δ was then obtained. P Δ P With virtual damping power P damp Subtract, multiply by 1 / Yes s The rotor angular acceleration was then obtained. s ( oh - oh s ).

[0015] More preferably, in the active power loop, during normal operation, the rotor angular acceleration... s ( oh - oh s (After integration) oh - oh s , and synchronous reference angular frequency oh s The summation yields the virtual synchronizer angular frequency. oh, Then, the internal potential phase reference value is obtained by integration. i ref .

[0016] More preferably, in the active power loop, during fault recovery, the rotor angular acceleration... s ( oh - oh s After the proportional link k d Get k d s ( oh - oh s Rotor angular acceleration s ( oh - oh s (After integration) oh - oh s , and synchronous reference angular frequency oh s The summation yields the virtual synchronizer angular frequency. oh, Then integrate with k d s ( oh - oh s The internal potential phase reference value is obtained by adding them together. i ref .

[0017] More preferably, in the active power loop, the angular frequency deviation ω- oh s As a complete frequency quantity, after subtracting the low-frequency component from the output of the first-order inertial element 1 / (1+As), only the mid-to-high frequency components reflecting the dynamic changes of the system are retained. These mid-to-high frequency components only exist during the dynamic process of the system and disappear during the steady state. The virtual damping power... P damp The output is zero.

[0018] The beneficial effects of this invention are: 1. The improved virtual damping power element and virtual inertia element of this invention have clear and explicit physical meanings. In the improved virtual damping power element, the virtual damping power is only applied when the system experiences disturbances or faults and requires virtual damping support. P damp The frequency is not zero, thus playing the role of virtual damping; while the angular frequency of the virtual synchronizer... oh Virtual damping power under constant steady-state conditions P damp The value is zero, corresponding to the fact that no virtual damping power is required in steady state. In the improved virtual inertia link, the system switches the corresponding control branch according to different operating conditions. During normal operation, the switch is connected to the 1 / s integral link, which, together with the active power loop, stabilizes the system frequency, simulating the inertia characteristics of a traditional synchronous machine. When a fault occurs, the switch is disconnected and no link is connected, forcing the system to operate at a fixed frequency. At the same time, current limiting and power angle stability are achieved by adjusting both the active power loop and the virtual impedance. Current limiting is achieved by increasing the virtual impedance. When the fault is recovered, the switch is connected to k... d The parallel branch of the proportional element and the 1 / s integral element enhances the damping effect while retaining the virtual inertia support, quickly suppressing power and frequency oscillations, and reducing the virtual impedance after fault recovery, allowing the system to gradually return to normal operation.

[0019] 2. This invention eliminates unnecessary power loss and errors in steady state. Traditional multi-machine parallel energy storage converters employ a virtual damping control strategy, directly multiplying the angular frequency deviation by the damping coefficient to obtain the damping power. This results in the damping power participating in power distribution in both steady state and dynamic states. Since the deviation of the multi-machine parallel system cannot be completely eliminated in steady state, the damping power persists, affecting the accuracy of active power distribution and reducing system operating efficiency. In contrast, the virtual damping power in this application is zero in steady state, eliminating unnecessary power loss and errors in steady state and improving system accuracy and steady-state efficiency.

[0020] 3. This invention improves the coordinated control of virtual damping and virtual inertia, which can prevent integral saturation and suppress overcurrent impact during faults, enhance damping to quickly smooth oscillations during fault recovery, and achieve current limiting and power angle stabilization through the coordinated control of virtual impedance and active power loop. It realizes frequency synchronization, power balance and stable output of multi-machine parallel system throughout the fault and recovery process, which greatly improves the fault ride-through capability and grid-connected adaptability of multi-machine parallel energy storage converter. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a fault ride-through method for a multi-machine parallel grid-connected energy storage converter according to the present invention; Figure 2 This is a topology diagram of the multi-machine parallel grid-connected energy storage converter of the present invention. Detailed Implementation

[0022] The relevant technologies of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0023] like Figure 1~2 As shown, this embodiment of the fault ride-through method for a multi-machine parallel grid-connected energy storage converter is used to simulate the damping of a traditional synchronous generator, generating virtual damping power. During fault occurrence and recovery, frequency synchronization and current limiting of the multi-machine parallel system are achieved through the active power loop, and then a modulation wave is generated together with the reactive power loop. The system includes: an improved virtual damping power loop and a virtual inertia loop; in the improved virtual damping power loop, the angular frequency... oh With synchronous reference angular frequency oh s difference( oh-oh s The difference between the first-order inertial element 1 / (1+As) and the damping coefficient is then calculated. D Multiply to obtain virtual damping power P damp Finally, in the power deviation Δ P Subtract virtual damping power P damp This achieves a virtual damping effect. Different control branches are switched according to different system operating conditions. During normal operation, the switch is connected to the 1 / s integral loop, working with the active power loop to stabilize the system frequency. In case of a fault, the switch is disconnected and no loop is connected, allowing the system to operate at a fixed frequency. Upon fault recovery, the switch is connected to the k... d A parallel branch connecting the proportional loop and the 1 / s integral loop rapidly suppresses power and frequency oscillations, gradually restoring the system to normal. The angle generated by the active power loop... i ref The modulated wave is obtained by combining the internal potential E output by the reactive power loop with the modulated wave, which ensures the stable operation of the multi-machine parallel energy storage converter system during fault ride-through.

[0024] In some embodiments, during normal operation, the active power control loop of the virtual synchronous generator simulates the oscillation equation of the rotor of a traditional synchronous generator, described by the following equation: (1) in, J This is a virtual moment of inertia; oh s The synchronous reference angular frequency has a value of 100π; oh The angular frequency of the virtual synchronizer; tFor time; P m For virtual mechanical power; P e For virtual electromagnetic power; P damp This represents the virtual damping power.

[0025] In some embodiments, during fault recovery, the switch is connected to k. d The branch in parallel with the proportional element and the 1 / s integral element is described by the following formula: (2) in, J This is a virtual moment of inertia; oh s The synchronous reference angular frequency has a value of 100π; oh The angular frequency of the virtual synchronizer; t For time; P m For virtual mechanical power; P e For virtual electromagnetic power; P damp For virtual damping power, k d This is the coefficient for the proportional element.

[0026] In some embodiments, virtual mechanical power in the active power control loop P m Subtract virtual electromagnetic power P e The power deviation Δ was then obtained. P Δ P With virtual damping power P damp Subtract, multiply by 1 / Yes s The rotor angular acceleration was then obtained. s ( oh - oh s ).

[0027] In some embodiments, during fault recovery, the rotor angular acceleration s ( oh - oh s After the proportional link k d Get k d s ( oh - oh s Rotor angular acceleration s ( oh - oh s (After integration, we obtain) oh - oh s ), and synchronous reference angular frequency oh s The summation yields the virtual synchronizer angular frequency. oh, Then integrate with k d s ( oh - oh s The internal potential phase reference value is obtained by adding them together. i ref .

[0028] In some embodiments, the angular frequency deviation (ω- oh s As a complete frequency quantity, after subtracting the low-frequency component of the first-order inertial element 1 / (1+As), only the mid-to-high frequency component reflecting the dynamic changes of the system is retained. This mid-to-high frequency component only exists during the dynamic process of the system. In steady state, the system frequency is stable, the mid-to-high frequency component disappears, and the virtual damping power... P damp The output is zero, consistent with the physical characteristics of a traditional synchronous machine damping winding.

[0029] The scaling factor in this embodiment k d It can enhance the system's damping ratio, effectively suppressing frequency oscillations; and increase the damping coefficient. D This can increase the virtual damping power at the moment of failure, thereby enhancing the effect of virtual damping. Parameters should be rationally designed according to actual needs. D and k d It can achieve good results.

[0030] The parameters of the virtual damping power element and the virtual inertia element in this embodiment can be flexibly designed. By adjusting the damping coefficient and the proportional coefficient, the magnitude of the virtual damping power can be adjusted to meet various needs.

[0031] The virtual damping power provided in this embodiment is adaptive. Angular frequency deviation (ω- oh s As a complete frequency quantity, after subtracting the low-frequency component of the first-order inertial element 1 / (1+As), only the mid-to-high frequency component reflecting the dynamic changes of the system is retained. This mid-to-high frequency component only exists during the dynamic process of the system. When the system frequency is stable in steady state, the mid-to-high frequency component disappears, which is consistent with the physical characteristics of the damping winding of the traditional synchronous machine. In summary, this invention, by improving the virtual damping power and virtual inertia links and combining them with adaptive switching control branches under different system operating conditions, achieves the characteristic that virtual damping exists dynamically and is zero in steady state. This effectively eliminates unnecessary power loss and errors in steady state, improving the averaging accuracy of active power and the system's operating efficiency. During faults, by forcing the system to operate at a fixed frequency and increasing the virtual impedance, integral saturation can be prevented and overcurrent surges suppressed. During the fault recovery phase, connecting parallel branches of the proportional and integral links enhances damping, quickly smoothing power and frequency oscillations while reducing virtual impedance to gradually restore the system to normal. The active and reactive power loops work together to generate modulation waves, ensuring frequency synchronization, power balance, and stable output of the multi-machine parallel energy storage converter system throughout the fault ride-through process. This significantly improves the system's fault ride-through capability and grid adaptability, providing reliable technical support for the stable operation of large-scale energy storage substations.

[0032] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A fault ride-through method for multi-machine parallel grid-connected energy storage converters, characterized in that, Frequency synchronization and current limiting of a multi-machine parallel system are achieved through an active power loop, and then the angle generated by the active power loop is... θ ref The modulated wave is obtained by combining the internal potential E output by the reactive power loop with the modulated wave to ensure the stable operation of the multi-machine parallel energy storage converter system during fault ride-through. During normal operation, the switches in the active power loop are connected to the 1 / s integral link, which works with the active power loop to stabilize the system frequency. When a fault occurs, the switches in the active power loop are disconnected and not connected to any link, and the system operates at a fixed frequency; During fault recovery, the switch in the active power loop is connected to k. d The proportional element and the 1 / s integral element are connected in parallel to quickly suppress power and frequency oscillations, allowing the system to gradually return to normal.

2. The fault ride-through method for a multi-machine parallel grid-connected energy storage converter according to claim 1, characterized in that, The active power loop is implemented as follows: virtual mechanical power P m With virtual electromagnetic power P e The difference Δ P With virtual damping power P damp After subtraction, the result is fed into the virtual inertia stage 1 / Jω s Virtual inertia element 1 / Jω s The switch selects the first 1 / s integral stage during normal operation, and the output... ω-ω s Enter k during fault recovery d The proportional element and the 1 / s integral element are connected in parallel in the branch, and the output of the 1 / s integral element is... ω-ω s ;in, ω-ω s After passing through a first-order inertial element 1 / (1+As), and then the damping coefficient D Multiply to form virtual damping power P damp ;at the same time, ω-ω s After the second 1 / s integral stage, and k d The output superposition yields the internal potential phase reference value. θ ref ; The reactive power loop is implemented by referencing reactive power. Q ref and actual reactive power Q After the difference is calculated, it passes through the proportional element k. Q And superimposed voltage amplification command E ref The internal potential E is obtained.

3. The fault ride-through method for a multi-machine parallel grid-connected energy storage converter according to claim 2, characterized in that, During normal operation, the fault ride-through method uses the following equation to simulate the oscillation equation of the rotor of a traditional synchronous generator in the active power control loop of the virtual synchronous generator: （1） In equation (1), J For virtual rotational inertia, ω s To synchronize the reference angular frequency, ω For the angular frequency of the virtual synchronizer, t For time, P m For virtual mechanical power, P e For virtual electromagnetic power, P damp This represents the virtual damping power.

4. The fault ride-through method for a multi-machine parallel grid-connected energy storage converter according to claim 2, characterized in that, When the fault recovery occurs, the switch connected to k in the fault-crossing method is... d The branch with the proportional element and the 1 / s integral element connected in parallel is represented by the following formula: （2） In equation (2), J For virtual rotational inertia, ω s To synchronize the reference angular frequency, ω For the angular frequency of the virtual synchronizer, t For time, P m For virtual mechanical power, P e For virtual electromagnetic power, P damp For virtual damping power, k d This is the coefficient for the proportional element.

5. The fault ride-through method for a multi-machine parallel grid-connected energy storage converter according to claim 2, characterized in that, In the active power loop, the virtual mechanical power P m Subtract virtual electromagnetic power P e The power deviation Δ was then obtained. P Δ P With virtual damping power P damp Subtract, multiply by 1 / Jω s The rotor angular acceleration was then obtained. s ( ω - ω s ).

6. The fault ride-through method for a multi-machine parallel grid-connected energy storage converter according to claim 5, characterized in that, In the active power loop, during normal operation, the rotor angular acceleration... s ( ω - ω s (After integration) ω - ω s , and synchronous reference angular frequency ω s The summation yields the virtual synchronizer angular frequency. ω, Then, the internal potential phase reference value is obtained by integration. θ ref .

7. The fault ride-through method for a multi-machine parallel grid-connected energy storage converter according to claim 5, characterized in that, In the active power loop, during fault recovery, the rotor angular acceleration... s ( ω - ω s After the proportional link k d Get k d s ( ω - ω s Rotor angular acceleration s ( ω - ω s (After integration) ω - ω s , and synchronous reference angular frequency ω s The summation yields the virtual synchronizer angular frequency. ω, Then integrate with k d s ( ω - ω s The internal potential phase reference value is obtained by adding them together. θ ref .

8. A fault ride-through method for a multi-machine parallel grid-connected energy storage converter according to claim 2, characterized in that, In the active power loop, the angular frequency deviation ω- ω s As a complete frequency quantity, after subtracting the low-frequency component from the output of the first-order inertial element 1 / (1+As), only the mid-to-high frequency components reflecting the dynamic changes of the system are retained. These mid-to-high frequency components only exist during the dynamic process of the system; they disappear during the steady state of the system. The virtual damping power... P damp The output is zero.

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