A method for controlling the parallel operation of multiple grid-connected energy storage converters

Abstract

This invention discloses a multi-machine parallel operation control method for grid-type energy storage converters, relating to the field of electrical engineering. The method involves establishing a sparse communication network; acquiring the frequency, RMS voltage, active power, and reactive power of each node, as well as the active and reactive power of neighboring nodes; constructing a grid-type converter control strategy combining active support and collaborative control; calculating the output frequency and RMS voltage of each grid-type converter; obtaining the three-phase AC voltage waveform through dq transformation, modulating it into a three-phase PWM switching control signal, and applying it to the grid-type converters to achieve the control effect. The active support of frequency and voltage in this invention addresses the deviation of frequency and voltage from rated values ​​in VSG control, while the collaborative control strategy eliminates the contradiction between power control and frequency / voltage control. The proposed optimized control method compensates for the deficiencies of VSG control, ensuring that the frequency and voltage of the grid-type converter are controlled at rated values ​​while accurately and rationally allocating active and reactive power.

Description

Technical Field

[0001] This invention relates to the field of electrical engineering, and specifically to a method for controlling the parallel operation of multiple units of a grid-type energy storage converter. Background Technology

[0002] With global climate change and the energy crisis stemming from the depletion of traditional fossil fuels, renewable energy has gained widespread attention due to its clean, green, and sustainable characteristics. These characteristics have driven the increasing electrification of modern power systems, but simultaneously lead to a gradual decrease in the inertia and damping capacity of power systems as the number of converters in the system increases. Compared to traditional generator sets, the dynamic characteristics of power electronic devices are fully controlled and rapid. When converters are widely used in power systems, the system exhibits a lack of inertia. Such low-inertia systems are prone to significant frequency shifts and excessively high rates of frequency change when facing interconnection line faults or imbalances between generation and load. This problem is even more severe for microgrids with a high proportion of renewable energy and power electronic devices.

[0003] To enhance the inertial support capability of converters in microgrids, Virtual Synchronous Generator (VSG) control has received widespread attention. VSG control is a grid-forming control mechanism that can be used to control grid-forming converters (GFCs) to participate in maintaining the frequency and voltage of the microgrid. It also simulates the operation of a synchronous generator rotor, giving the GFC inertial characteristics and providing inertial support for the microgrid. Furthermore, VSGs mimic the power-sharing capability of synchronous generators by performing frequency and voltage droop control, allowing them to distribute power among distributed sources based on rated power and droop factor.

[0004] While VSG control can maintain microgrid frequency and voltage and perform power distribution, its functionality has limitations. VSG control achieves power distribution through frequency and voltage droop, which can cause the frequency and voltage of the grid-connected converter (GFC) to deviate from their rated values. This deviation is exacerbated by the uncertainty of new energy output and the significant load fluctuations in microgrids, impacting power quality and posing challenges to the stable operation of the microgrid. Furthermore, the effectiveness of power distribution is severely affected by line impedance; when the line impedances of different grid-connected converters (GFCs) differ significantly, the power distribution accuracy becomes very poor. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a multi-machine parallel operation control method for grid-connected energy storage converter systems. This method comprises two parts: active frequency and voltage support and collaborative control based on multi-agent theory. The active frequency and voltage support addresses the deviation of frequency and voltage from their rated values ​​in VSG control, while the collaborative control eliminates the contradiction between power control and frequency / voltage control. The proposed optimized control method compensates for the deficiencies of VSG control, ensuring that the frequency and voltage of the grid-connected converter (GFC) are controlled at their rated values ​​while accurately and rationally allocating active and reactive power.

[0006] A method for controlling the parallel operation of multiple grid-connected energy storage converters includes the following steps:

[0007] S1. For an AC microgrid system containing grid-type converters, establish a sparse communication network to realize information interaction between different grid-type converters in the AC microgrid system; the information includes active power and reactive power; in the sparse communication network, each grid-type converter is treated as a node, and if there is a communication connection between two nodes, they are said to be adjacent or neighboring nodes.

[0008] S2: Based on the established sparse communication network, each node measures its own three-phase output voltage and output current, calculates its own frequency, voltage RMS value, active power and reactive power, and communicates with neighboring nodes in the sparse communication network to obtain the active power and reactive power of neighboring nodes.

[0009] S3: Based on VSG control, active support control for frequency and voltage and coordinated control for active and reactive power are added to construct a grid-type converter control strategy that combines active support and coordinated control. Based on the obtained node frequency, effective voltage value, active and reactive power, as well as the active and reactive power of neighboring nodes, the target values ​​of the output frequency and output voltage of each grid-type converter in the AC microgrid system in the dq0 coordinate system are calculated using the grid-type converter control strategy that combines active support and coordinated control. The target values ​​of the output voltage of each grid-type converter are adjusted through virtual impedance control and voltage loop and current loop control.

[0010] The grid-type converter control strategy combining active support and coordinated control includes:

[0011] The expression for active frequency support and coordinated active power control for all grid-type converters is as follows:

[0012]

[0013] Among them, GFC i For the i-th grid-type converter, GFC jLet ω be the j-th grid-type converter, where i and j are the numbers of the grid-type converter. i For GFC i angular frequency, ω vi For GFC i The frequency command value controlled by VSG, e ωi For GFC i The frequency adjustment term, J is the moment of inertia, D is the damping coefficient, t is time, and P is the frequency adjustment term. mi For GFC i The active power reference value, P refi For GFC i The rated value of active power, K ωi For GFC i The active angular frequency droop coefficient, α i For GFC i Frequency active support coefficient, ω n P is the rated angular frequency. i For GFC i The active power, P j For GFC j The active power, N i For the neighborhood set, d ij Weights among grid-type converters;

[0014] Select a leader from all grid-connected converters. Active voltage support is provided only to the selected leader, while reactive power is coordinated across all grid-connected converters. The expression is:

[0015]

[0016] Among them, Q m Q is the reactive power reference value. ref U is the rated reactive power, Q is the reactive power output of VSG, and U is the reactive power of VSG. n Where U is the rated voltage, E is the output voltage of the VSG, and U is the rated voltage of the voltage rating. d K represents the d-axis component of the voltage command value. v K is the reactive voltage droop factor, and K is the integral factor. E is the integral symbol; v For the voltage command value controlled by VSG, e U For voltage regulation, β is the active voltage support coefficient; Q i For GFC i reactive power, Q j For GFC j reactive power;

[0017] The virtual impedance control is expressed as follows:

[0018]

[0019] In the formula, r v and L v These are virtual resistance and inductance, u od * For virtual impedance control of the output on the d-axis, u oq * For virtual impedance control of the output on the q-axis, i od i represents the d-axis component of the VSG output current. oq E is the q-axis component of the VSG output current. q The q-axis component of the voltage command value;

[0020] The expression for adjusting the target value of the output voltage using the voltage loop and current loop control is as follows:

[0021]

[0022] Among them, u vd * This represents the voltage loop output on the d-axis; u vq * This is the output of the voltage loop on the q-axis; u id * This represents the output of the current loop on the d-axis; u iq * This is the output of the current loop on the q-axis; u d The output voltage of the VSG on the d-axis; u q C is the output voltage of the VSG on the q-axis. f and L f These are the inductance and capacitance parameters of the filter, respectively; G pi (s) is a PI controller for the current loop, k pi It is the proportional parameter of the current loop, k ii It is the integral parameter of the current loop; G pu (s) is a PI controller for the voltage loop, k pu It is the proportional parameter of the voltage loop, k iu These are the integral parameters of the voltage loop; i d i represents the output current of the VSG on the d-axis. q This represents the output current of the VSG on the q-axis.

[0023] S4: The target voltage value and output frequency obtained by the grid-type converter control strategy combining active support and coordinated control are transformed into a three-phase AC voltage waveform through dq transformation, and then further modulated into a three-phase PWM switching control signal, which is applied to the grid-type converter to achieve the control effect.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. This invention proposes an improved method for VSG-controlled grid-type converters. This method is aimed at VSG control, which is widely used in grid-type converters, and does not make any changes to the structure and parameters of VSG control itself. It can be directly applied to grid-type converters based on VSG control.

[0026] 2. This invention proposes an active frequency and voltage support method for grid-type converters. This method can accurately control the frequency and voltage of grid-type converters at their rated values, thus overcoming the shortcomings of VSG control.

[0027] 3. This invention, combining multi-agent consensus theory, proposes a multi-machine parallel cooperative control method for grid-connected converters. The proposed method can improve the distribution of active and reactive power among different grid-connected converters (GFCs), enabling precise allocation according to the expected target. Simultaneously, it employs a sparse communication network for information exchange, reducing the communication burden. Attached Figure Description

[0028] Figure 1 This is a basic working principle diagram of VSG and a multi-machine parallel operation control method for a grid-type energy storage converter in an embodiment of the present invention;

[0029] Figure 2 This is a general control block diagram of a multi-machine parallel operation control method for a grid-type energy storage converter according to an embodiment of the present invention;

[0030] Figure 3 This is a circuit diagram of a single bus topology selected in an embodiment of the present invention to verify a multi-machine parallel operation control method for a grid-type energy storage converter.

[0031] Figure 4 This is a circuit diagram of a mesh topology selected in an embodiment of the present invention to verify a multi-machine parallel operation control method for a grid-type energy storage converter;

[0032] Figure 5 The figure shows the experimental results of a hardware-in-the-loop (HIL) simulation experiment on a multi-machine parallel operation control method using a grid-type energy storage converter for a single-bus topology multi-parallel converter system in an embodiment of the present invention.

[0033] Among them, (a) is the effect diagram of active frequency support under a single bus topology, (b) is the active power coordinated control diagram, (c) is the reactive power coordinated control effect diagram, and (d) is the voltage active support effect diagram.

[0034] Figure 6The figure shows the experimental results of a HIL simulation experiment on a multi-machine parallel operation control method using a grid-type energy storage converter for a multi-parallel converter system with a mesh topology in an embodiment of the present invention.

[0035] Among them, (a) is the effect diagram of active frequency support under the mesh topology, (b) is the active power coordinated control diagram, (c) is the reactive power coordinated control effect diagram, and (d) is the voltage active support effect diagram. Detailed Implementation

[0036] This invention provides a multi-machine parallel operation control method for grid-type energy storage converters. It applies active support control of frequency and voltage to the converters controlled by VSG to prevent them from deviating from the rated values. At the same time, it introduces a power cooperative control method based on multi-agent theory to achieve the goal of accurately allocating active and reactive power without hindering the effect of frequency and voltage control.

[0037] like Figure 1 and Figure 2 As shown, a multi-machine parallel operation control method for a grid-type energy storage converter includes the following steps:

[0038] S1. For an AC microgrid system containing grid-type converters, establish a sparse communication network to realize information exchange between different grid-type converters (GFCs) in the AC microgrid system; the information includes active power and reactive power;

[0039] The basic components of the AC microgrid system are grid-type converters, filter circuits, line impedances, and loads. Different grid-type converters will have different output impedances to better reflect actual conditions.

[0040] The sparse communication network refers to a communication network in an AC microgrid system where the number of communication connections between different grid-type converters (GFCs) is less than the number of electrical connections, but connectivity can still be guaranteed. In the sparse communication network, each grid-type converter is treated as a node. If there is a communication connection between two nodes, they are said to be adjacent or neighboring nodes.

[0041] This embodiment analyzes single-busbar topology and mesh topology respectively. The two topology diagrams are as follows: Figure 3 and Figure 4 As shown in the figure. The power of both loads is P = 20000W and Q = 10000Var, where P is the active power and Q is the reactive power. The dashed line represents the communication link between grid converters (GFCs). Each grid converter (GFC) only exchanges information with the grid converters (GFCs) connected to the communication link. The specific parameters of the AC microgrid system are shown in the table below. Each grid converter (GFC) has a different equivalent output impedance.

[0042] Table 1 Specific parameters of the AC microgrid system

[0043]

[0044] S2: Based on the established sparse communication network, each node measures its own three-phase output voltage and output current, calculates its own frequency, voltage RMS value, active power and reactive power, and communicates with neighboring nodes in the sparse communication network to obtain the active power and reactive power of neighboring nodes. After this process, the node obtains its own frequency, voltage RMS value, active power and reactive power, as well as the active power and reactive power of neighboring nodes, which will be used in the proposed parallel control strategy for multi-grid converters.

[0045] S3: Based on VSG control, active support control for frequency and voltage and coordinated control for active and reactive power are added to construct a grid-type converter control strategy that combines active support and coordinated control. Based on the obtained node frequency, effective voltage value, active and reactive power, as well as the active and reactive power of neighboring nodes, the target values ​​of the output frequency and output voltage of each grid-type converter in the AC microgrid system in the dq0 coordinate system are calculated using the grid-type converter control strategy that combines active support and coordinated control. The target values ​​of the output voltage of each grid-type converter are adjusted through virtual impedance control and voltage loop and current loop control.

[0046] Traditional methods implement VSG control for grid-type converters and use virtual impedance control to improve their power distribution capability;

[0047] VSG control is a type of grid-based control that maintains the bus frequency and voltage of an AC microgrid system by controlling the frequency and effective voltage of grid-based converters (GFCs) and achieves a reasonable distribution of power among different grid-based converters (GFCs). It includes two parts: active power-frequency control and reactive power-voltage control.

[0048] VSG performs active-frequency control by simulating the rotor motion equations of a synchronous generator, specifically as follows:

[0049]

[0050] In the formula, ω is the angular frequency of the VSG, ω n Where ω is the rated angular frequency, J is the moment of inertia, D is the damping coefficient, and P is the rated angular frequency. m P is the active power reference value, where P is the active power output of VSG. ref K represents the rated value of active power. ω The active angular frequency droop coefficient is t, where t is time.

[0051] It can be seen that when VSG is in steady state, P = P m =P ref +K ω (ω n -ω), the purpose of this design is to achieve a reasonable distribution of active power by controlling the frequency of each grid converter (GFC), but it will cause the frequency to deviate from the rated value;

[0052] The reactive-voltage control of the VSG simulates the electromagnetic characteristics of a synchronous generator, aiming to achieve a reasonable distribution of reactive power among different grid-type converters (GFCs) operating in parallel.

[0053]

[0054] In the formula, Q m Q is the reactive power reference value. ref U is the rated reactive power, Q is the reactive power output of VSG, and U is the reactive power of VSG. n Where U is the rated voltage, E is the output voltage of the VSG, and U is the rated voltage of the voltage rating. d K represents the d-axis component of the voltage command value. v K is the reactive voltage droop factor, and K is the integral factor. The integral symbol is used.

[0055] When VSG is in steady state, Q = Q m =Q ref +K v (U n Similar to active-frequency control, the -U) method distributes reactive power while causing the output voltage of the grid converter (GFC) to deviate from its rated value.

[0056] The active and reactive power output by the VSG are obtained by passing the instantaneous power of the VSG through a low-pass filter (LPF).

[0057] In VSG control, virtual impedance is often used to mitigate the impact of differences in output impedance between different grid-type converters (GFCs). A suitable virtual impedance can decouple active and reactive power, thus improving power distribution. The expression for virtual impedance control is as follows:

[0058]

[0059] In the formula, r v and L v These are virtual resistance and inductance, u od * For virtual impedance control of the output on the d-axis, u oq *For virtual impedance control of the output on the q-axis, i od i represents the d-axis component of the VSG output current. oq E is the q-axis component of the VSG output current. q The q-axis component of the voltage command value;

[0060] To avoid voltage and current fluctuations, voltage loops and current loops are typically used to control the output voltage and current of a grid-connected converter (GFC).

[0061]

[0062] Among them, u vd * This represents the voltage loop output on the d-axis; u vq * This is the output of the voltage loop on the q-axis; u id * This represents the output of the current loop on the d-axis; u iq * This is the output of the current loop on the q-axis; u d The output voltage of the VSG on the d-axis; u q C is the output voltage of the VSG on the q-axis. f and L f These are the inductance and capacitance parameters of the filter, respectively; G pi (s) is a PI controller for the current loop, k pi It is the proportional parameter of the current loop, k ii It is the integral parameter of the current loop; G pu (s) is a PI controller for the voltage loop, k pu It is the proportional parameter of the voltage loop, k iu These are the integral parameters of the voltage loop; i d i represents the output current of the VSG on the d-axis. q This refers to the output current of the VSG on the q-axis.

[0063] Based on VSG control, active frequency and voltage support is implemented to restore the frequency and voltage of the grid-connected converter (GFC) to their rated values:

[0064] VSG-controlled grid converters regulate active and reactive power by changing frequency and voltage. However, this regulation method causes the frequency and voltage of the grid converter to deviate from their rated values, reducing power quality. To address this issue, active frequency and voltage support is required for the grid converter.

[0065] Active frequency and voltage support for grid-connected converters is achieved by adding active frequency and voltage support terms to the VSG control. This support term changes the steady-state state of the VSG control to bring the frequency and voltage back to their rated values. The relationship between the added VSG frequency and active power can be expressed as follows:

[0066]

[0067] In the formula, ω v For the frequency command value controlled by VSG, e ω For frequency adjustment, α is the active frequency support coefficient;

[0068] The relationship between voltage and reactive power can be expressed as:

[0069]

[0070] In the formula, E v For the voltage command value controlled by VSG, e U For voltage regulation, β is the active voltage support coefficient;

[0071] When the derivatives of all integrated variables are zero, the AC microgrid system enters a steady state. It can be deduced that the steady state of the VSG, including the active frequency and voltage support terms, satisfies:

[0072]

[0073] It can be seen that through this active frequency and voltage support method, the steady-state frequency and voltage of the VSG will be controlled to their rated values. However, this will also change the original droop control mode of the VSG, making the VSG's ability to distribute active and reactive power worse, resulting in a steady-state deviation in the distribution of active and reactive power.

[0074] Each grid-connected converter (GFC) exchanges power information of other grid-connected converters (GFCs) required for the cooperative control strategy based on sparse communication networks and multi-agent consensus theory, and performs cooperative control of active and reactive power to achieve precise allocation of active and reactive power among the GFCs.

[0075] Multi-agent consensus theory is a mathematical theory and methodology that studies how multiple autonomous agents in a distributed system can reach consensus or act in unison through mutual communication and adjustment. The core of the theory is designing algorithms and protocols, utilizing communication networks, to enable each agent to exchange local information and execute adjustment strategies, ultimately achieving consistent behavior or state throughout the system.

[0076] For a sparse communication network with n nodes, if there exists a communication link ij connecting GFC... i and GFCj GFC j Considered as being in the neighborhood set N i In the middle, j∈N i GFC i Only from the communication coefficient a ij The neighborhood set N of 1 i Receive information in, otherwise a ij =0. The symmetric n×n order adjacency equation A = (a ij ) n×n It is stated that GFC i For the i-th grid-type converter, GFC j Let i be the j-th grid-type converter, where i and j are the numbers of the grid-type converter.

[0077] Define the weights between network converters (GFC):

[0078]

[0079] Where, d ij For GFC i With GFC j Weights between them;

[0080] Furthermore, the Laplace matrix of a sparse communication network is L = (l ij ) n×n :

[0081]

[0082] Among them, l ij For the off-diagonal elements of the Laplace matrix, l ii Diagonal elements;

[0083] This invention employs a consensus algorithm to design the interaction of neighboring information, with the consensus variable x of each node being... i The consistency variable x of any neighboring node is adjusted based on the consistency variables of its neighboring nodes. As the number of iterations increases, the consistency variable x of any neighboring node... i x j tending to be consistent, satisfying |x i (k)-x j (k)|→0, the AC microgrid system converges when the state variables of all nodes reach consistency within the convergence condition range. The first-order consensus algorithm is described as follows:

[0084]

[0085] In the formula, x i Let i be a consistent variable, i = 1, 2, ..., n. For the consistency variable x i The differential;

[0086] The control strategy proposed in this invention uses frequency, voltage, active power, and reactive power as adjustment targets. Since the adjustment targets of frequency and voltage are only related to the rated values ​​and can be completed without information interaction, the active and reactive power of the grid converter (GFC) can be used as adjustment targets. Based on the local state variables of the grid converter (GFC) and the state variables of neighboring grid converters (GFC), the coordinated control of the state variables of each grid converter (GFC) is achieved through a consensus algorithm.

[0087] It can be seen that after adding the frequency and voltage active support terms, the original Pf droop relationship of the VSG is disrupted, and the VSG control can no longer achieve reasonable allocation of active power. Furthermore, for islanded systems, accurate reactive power allocation requires a certain voltage difference between each grid-connected converter (GFC), which contradicts controlling the voltage of all GFCs to their rated values. Therefore, the aforementioned frequency and voltage active support method must be improved to ensure that active and reactive power are allocated according to the expected target without affecting the frequency and voltage active support function.

[0088] According to the multi-agent consensus theory, a consensus algorithm of the form shown below can achieve the goal of evenly distributing active and reactive power among various grid-connected converters (GFCs):

[0089]

[0090] Among them, P i For GFC i The active power, Q i For GFC i reactive power, P j For GFC j The active power, Q j For GFC j reactive power, For P i The derivative of For Q i The derivative;

[0091] However, grid-type converters cannot directly control active and reactive power. For parallel systems of multiple grid-type converters with approximately purely inductive line impedance, the goal of changing their active and reactive power is generally achieved by controlling the frequency to change their phase and controlling the voltage command value to change their output voltage. Therefore, the consensus algorithm with the objective of evenly distributing active and reactive power is rewritten as follows:

[0092]

[0093] Where, ωi For GFC i angular frequency, E di For GFC i The d-axis component of the voltage command value;

[0094] By combining power cooperative control based on multi-agent theory with active frequency-voltage support terms, the new VSG control frequency expression is as follows:

[0095]

[0096] Where, ω vi For GFC i The frequency command value controlled by VSG, e ωi For GFC i Frequency adjustment term, P mi For GFC i The active power reference value, P refi For GFC i The rated value of active power, K ωi For GFC i The active angular frequency droop coefficient, α i For GFC i The frequency active support coefficient;

[0097] At this point, the steady-state values ​​of frequency and active power of each grid-connected converter (GFC) will satisfy:

[0098]

[0099] That is, the frequency of each grid-connected converter (GFC) is controlled at the rated value, and the active power can be distributed as expected.

[0100] Since precise reactive power distribution requires a certain voltage difference between each grid-connected converter (GFC), which contradicts the requirement to control the voltage of all GFCs to their rated values, it is necessary to select a leader from all GFCs. Active voltage support is provided only to the selected leader GFC, while reactive power coordinated control is implemented for all GFCs. The expression is as follows:

[0101]

[0102] At this point, the steady-state voltage and reactive power of each grid-connected converter (GFC) will conform to:

[0103]

[0104] In the formula, U leader The selected voltage actively supports the output voltage of the leader;

[0105] This invention addresses the scenario of multiple converters operating in parallel in a grid-connected configuration. Based on VSG control, it implements an active frequency and voltage support method and a power collaborative control method based on a sparse communication network. This method overcomes the shortcomings of VSG control, achieves error-free recovery of the converter's frequency and voltage, and precise allocation of active and reactive power, thus achieving optimal control performance.

[0106] S4: The target voltage value and output frequency obtained by the grid-type converter control strategy combining active support and coordinated control are transformed into a three-phase AC voltage waveform through dq transformation, and then further modulated into a three-phase PWM switching control signal, which is applied to the grid-type converter to achieve the control effect.

[0107] Figure 5 The simulation results show four processes under a single-bus topology, namely: Figure 5 (a) When t = 2s, frequency active support control is added on the basis of general VSG control, and each GFC frequency is controlled to the rated value. Figure 5 (b) Before t=8s, due to the influence of frequency active support control, the active power of each GFC is no longer reasonably distributed. At t=8s, active power collaborative control is added to make the active power of each GFC redistribute correctly. Figure 5 (c) When t = 15s, reactive power coordination control is added. Relying solely on VSG control cannot accurately allocate reactive power according to the expected target, resulting in a deviation. This deviation is eliminated after reactive power coordination control is added. Figure 5 (d) At t = 20s, active voltage support is applied to the leader, and the leader voltage is controlled to the rated value.

[0108] Figure 6 To adopt Figure 4 Simulation results for the mesh topology shown: Figure 6 (a) When t = 2s, frequency active support control is added on the basis of general VSG control, and each GFC frequency is controlled to the rated value. Figure 6 (b) When t = 8s, active power coordination control is added, and the active power of each GFC is correctly redistributed; Figure 6 (c) At t=15s, reactive power collaborative control is added, and reactive power is precisely allocated; Figure 6 (d) At t = 20s, active voltage support is applied to the leader, and the leader voltage is controlled to the rated value.

[0109] Depend on Figure 5 and Figure 6It can be seen that, through a sparse communication network, the frequency and voltage active support and power sharing control strategy proposed in this invention can accurately control the frequency and voltage of the grid-type converter at the rated value, while achieving precise distribution of active and reactive power among different GFCs.

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for controlling the parallel operation of multiple units in a grid-connected energy storage converter, characterized in that, Includes the following steps: S1. For AC microgrid systems containing grid-type converters, establish a sparse communication network to realize information exchange between different grid-type converters in the AC microgrid system. S2: Based on the established sparse communication network, each node measures its own three-phase output voltage and output current, calculates its own frequency, voltage RMS value, active power and reactive power, and communicates with neighboring nodes in the sparse communication network to obtain the active power and reactive power of neighboring nodes. S3: Based on VSG control, active support control for frequency and voltage and coordinated control for active and reactive power are added to construct a grid-type converter control strategy that combines active support and coordinated control. Based on the obtained node frequency, effective voltage value, active and reactive power, as well as the active and reactive power of neighboring nodes, the target values ​​of the output frequency and output voltage of each grid-type converter in the AC microgrid system in the dq0 coordinate system are calculated using the grid-type converter control strategy that combines active support and coordinated control. The target values ​​of the output voltage of each grid-type converter are adjusted through virtual impedance control and voltage loop and current loop control. S4: The target voltage value and output frequency obtained by the grid-type converter control strategy combining active support and coordinated control are transformed into a three-phase AC voltage waveform through dq transformation, and then further modulated into a three-phase PWM switching control signal, which is applied to the grid-type converter to achieve the control effect.

2. The multi-machine parallel operation control method for a grid-type energy storage converter according to claim 1, characterized in that, The information includes active power and reactive power; in the sparse communication network, each grid-type converter is treated as a node, and if there is a communication connection between two nodes, they are said to be adjacent or neighboring nodes.

3. The multi-machine parallel operation control method for a grid-type energy storage converter according to claim 1, characterized in that, The grid-type converter control strategy combining active support and coordinated control described in S3 includes: performing active frequency support and coordinated active power control on all grid-type converters; selecting a leader from all grid-type converters, performing active voltage support only on the selected leader grid-type converter, and performing coordinated reactive power control on all grid-type converters.

4. The multi-machine parallel operation control method for a grid-type energy storage converter according to claim 3, characterized in that, The expression for the coordinated control of frequency active support and active power for all grid-type converters is as follows: Among them, GFC i For the i-th grid-type converter, GFC j Let ω be the j-th grid-type converter, where i and j are the numbers of the grid-type converter. i For GFC i angular frequency, ω vi For GFC i The frequency command value controlled by VSG, e ωi For GFC i The frequency adjustment term, J is the moment of inertia, D is the damping coefficient, t is time, and P is the frequency adjustment term. mi For GFC i The active power reference value, P refi For GFC i The rated value of active power, K ωi For GFC i The active angular frequency droop coefficient, α i For GFC i Frequency active support coefficient, ω n P is the rated angular frequency. i For GFC i The active power, P j For GFC j The active power, N i For the neighborhood set, d ij The weights between grid-type converters.

5. The multi-machine parallel operation control method for a grid-type energy storage converter according to claim 3, characterized in that, The expression for selecting a leader from all grid-connected converters, providing active voltage support only to the selected leader, and simultaneously performing coordinated reactive power control on all grid-connected converters is as follows: Among them, Q m Q is the reactive power reference value. ref U is the rated reactive power, Q is the reactive power output of VSG, and U is the reactive power of VSG. n Where U is the rated voltage, E is the output voltage of the VSG, and U is the rated voltage of the voltage rating. d K represents the d-axis component of the voltage command value. v K is the reactive voltage droop factor, and K is the integral factor. E is the integral symbol; v For the voltage command value controlled by VSG, e U For voltage regulation, β is the active voltage support coefficient; Q i For GFC i reactive power, Q j For GFC j The reactive power.

6. The multi-machine parallel operation control method for a grid-type energy storage converter according to claim 1, characterized in that, The expression for the virtual impedance control is: In the formula, r v and L v These are virtual resistance and inductance, u od * For virtual impedance control of the output on the d-axis, u oq * For virtual impedance control of the output on the q-axis, i od i represents the d-axis component of the VSG output current. oq E is the q-axis component of the VSG output current. q This represents the q-axis component of the voltage command value.

7. The multi-machine parallel operation control method for a grid-type energy storage converter according to claim 1, characterized in that, The expression for adjusting the target value of the output voltage using the voltage loop and current loop control is as follows: Among them, u vd * This represents the voltage loop output on the d-axis; u vq * This is the output of the voltage loop on the q-axis; u id * This represents the output of the current loop on the d-axis; u iq * This is the output of the current loop on the q-axis; u d The output voltage of the VSG on the d-axis; u q C is the output voltage of the VSG on the q-axis. f and L f These are the inductance and capacitance parameters of the filter, respectively; G pi (s) is a PI controller for the current loop, k pi It is the proportional parameter of the current loop, k ii It is the integral parameter of the current loop; G pu (s) is a PI controller for the voltage loop, k pu It is the proportional parameter of the voltage loop, k iu These are the integral parameters of the voltage loop; i d i represents the output current of the VSG on the d-axis. q This represents the output current of the VSG on the q-axis.

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