Multi-machine parallel operation control method of network construction type energy storage converter

Abstract

The invention discloses a multi-machine parallel operation control method for a network-forming type energy storage converter, and relates to the field of electrical engineering. Establishing a sparse communication network; obtaining the frequency, the voltage effective value, the active power and the reactive power of the node and the active power and the reactive power of a neighbor node; constructing a network construction type converter control strategy combining active support and cooperative control, and calculating the output frequency and voltage effective value of each network construction type converter; and obtaining a three-phase AC voltage waveform through dq conversion, modulating the three-phase AC voltage waveform into a three-phase PWM switch control signal, and applying the three-phase PWM switch control signal to the network-forming converter to achieve a control effect. The active support of the frequency and the voltage aims at the deviation of the frequency and the voltage to rated values in the VSG control, the contradiction between the power control and the frequency and voltage control is eliminated by the cooperative control strategy, the defects of the VSG control are made up by the proposed optimization control method, the frequency and the voltage of the network construction type converter are controlled to be the rated values, and meanwhile, the efficiency of the network construction type converter is improved. And the active power and the reactive power can be accurately and reasonably distributed.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering, and in particular to a multi-machine parallel operation control method for a grid-type energy storage converter. Background Art

[0002] With global climate change and the energy crisis caused by the depletion of traditional fossil energy, renewable energy has attracted widespread attention due to its clean, green and sustainable characteristics. These characteristics have promoted the electronicization of modern power systems, but at the same time, the inertia and damping capacity of the power system will gradually weaken as the number of converters in the system increases. Compared with traditional generator sets, the dynamic characteristics of power electronic equipment are fully controlled and fast. When converters are used more in power systems, the system will show a lack of inertia. This low-inertia system is often prone to large frequency deviations and excessive frequency change rates when facing interconnection line failures or imbalances between power generation and load. This problem is even more serious for microgrids where renewable energy and power electronic equipment account for a high proportion.

[0003] In order to improve the inertial support capability of converters in microgrids, virtual synchronous generator (VSG) control has received extensive attention. VSG control is a grid-forming control that can be used to control grid-forming converters (GFCs) to participate in the maintenance of microgrid frequency and voltage. It also enables grid-forming converters to simulate the working process of synchronous generator rotors, giving them inertial characteristics and providing inertial support for microgrids. In addition, VSG also imitates the power sharing capability of synchronous generators by performing frequency and voltage droop control, which enables it to distribute power among distributed power sources according to rated power and droop coefficient.

[0004] Although VSG control can maintain the frequency and voltage of the microgrid and distribute power, its function is flawed. VSG control achieves power distribution by drooping the frequency and voltage, which will cause the frequency and voltage of the GFC to deviate from the rated value. Due to the uncertainty of the output of new energy and the large load fluctuations in the microgrid, this deviation will be more serious, affecting the power quality and posing challenges to the stable operation of the microgrid. At the same time, the effect of power distribution is seriously affected by the line impedance. When the line impedance of different GFCs is greatly different, the power distribution accuracy will become very poor. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a multi-machine parallel operation control method for a grid-type energy storage converter system, including two parts: active frequency and voltage support and collaborative control based on multi-agent theory. The active frequency and voltage support is aimed at the deviation of frequency and voltage from the rated values ​​in VSG control, and the collaborative control eliminates the contradiction between power control and frequency and voltage control. The proposed optimization control method makes up for the defects of VSG control. While ensuring that the frequency and voltage of the grid-type converter (GFC) are controlled at the rated values, the active and reactive power can be accurately and reasonably distributed.

[0006] A multi-machine parallel operation control method for a grid-type energy storage converter comprises the following steps:

[0007] S1. For an AC microgrid system including a meshed converter, a sparse communication network is established for realizing information exchange between different meshed converters in the AC microgrid system; the information includes active power and reactive power; each meshed converter is regarded as a node in the sparse communication network, and if there is a communication connection between two nodes, they are called 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 respectively, obtains its own frequency, voltage RMS, active power and reactive power through calculation, and communicates with neighboring nodes in the sparse communication network to obtain the active power and reactive power of neighboring nodes;

[0009] S3: On the basis of VSG control, active support control of frequency and voltage and coordinated control of active and reactive power are added to construct a grid-type converter control strategy combining active support and coordinated control. Based on the acquired node frequency, voltage effective value, active power and reactive power, as well as the active and reactive power of neighboring nodes, the grid-type converter control strategy combining active support and coordinated control is used to calculate 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, and the output voltage target value of each grid-type converter is adjusted through virtual impedance control and voltage loop and current loop control.

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

[0011] Active frequency support and coordinated active power control are performed on all grid-connected converters. The expression is:

[0012]

[0013] Among them, GFC i is the i-th grid-connected converter, GFC jis the jth grid-type converter, i and j are the numbers of the grid-type converter, ω i For GFC i The angular frequency, ω vi For GFC i The frequency command value of VSG control, e ωi For GFC i The frequency adjustment term, J is the moment of inertia, D is the damping coefficient, t is the time, P mi For GFC i Active power reference value, P refi For GFC i Rated value of active power, K ωi For GFC i Active angular frequency droop coefficient, α i For GFC i The frequency active support coefficient, ω n is the rated angular frequency, P i For GFC i Active power, P j For GFC j Active power, N i is the neighborhood set, d ij is the weight between the grid-forming converters;

[0014] A leader is selected from all grid-connected converters, and voltage is actively supported only for the grid-connected converter selected as the leader. Meanwhile, reactive power is coordinated controlled for all grid-connected converters. The expression is:

[0015]

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

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

[0018]

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

[0020] The expression for adjusting the output voltage target value by the voltage loop and current loop control is:

[0021]

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

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

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

[0025] 1. The present invention proposes an improvement method for a VSG-controlled grid-type converter. 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 the VSG control itself. It can be directly applied to a grid-type converter based on VSG control.

[0026] 2. The present invention proposes a method for actively supporting the frequency and voltage of a grid-type converter. This method can accurately control the frequency and voltage of the grid-type converter within the rated value, thus making up for the defects of VSG control.

[0027] 3. The present invention combines the multi-agent consistency theory and proposes a multi-machine parallel coordinated control method for a grid-type converter. The proposed method can improve the distribution of active and reactive power between different grid-type converters (GFCs) so that it can be accurately distributed according to the expected goals. At the same time, a sparse communication network is used for information exchange, which reduces the communication burden. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 It is an overall control block diagram of a multi-machine parallel operation control method of a grid-type energy storage converter in an embodiment of the present invention;

[0030] Figure 3 A circuit diagram of a single busbar topology structure selected for verifying a multi-machine parallel operation control method of a grid-type energy storage converter in an embodiment of the present invention;

[0031] Figure 4 A circuit diagram of a mesh topology structure selected in an embodiment of the present invention for verifying a multi-machine parallel operation control method of a mesh-type energy storage converter;

[0032] Figure 5 The figure is an experimental result of a hardware-in-the-loop (HIL) experiment of a multi-machine parallel operation control method of 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 frequency active support effect diagram under the single bus topology structure, (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 6This is a diagram of experimental results of a HIL simulation experiment of a multi-machine parallel operation control method using a grid-type energy storage converter for a mesh topology multi-parallel converter system according to an embodiment of the present invention;

[0035] Among them, (a) is the frequency active support effect diagram under the mesh topology structure, (b) is the active power collaborative control diagram, (c) is the reactive power collaborative control effect diagram, and (d) is the voltage active support effect diagram. DETAILED DESCRIPTION

[0036] The present invention provides a multi-machine parallel operation control method for a grid-type energy storage converter, which applies active support control of frequency and voltage to the converter controlled by VSG so that it no longer deviates from the rated value. At the same time, a power collaborative control method based on multi-agent theory is introduced to achieve the goal of accurately distributing active and reactive power without hindering the frequency and voltage control effects.

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

[0038] S1. For an AC microgrid system including a grid-forming converter, a sparse communication network is established for realizing information interaction between different grid-forming converters (GFCs) in the AC microgrid system; the information includes active power and reactive power;

[0039] The AC microgrid system is basically composed of a grid-forming converter, a filter circuit, a line impedance and a load, wherein different grid-forming converters have different output impedances to better meet actual conditions;

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

[0041] This embodiment analyzes the single bus topology and the mesh topology respectively. The two topologies are shown in FIG. Figure 3 and Figure 4 As shown. The power of the two loads is P = 20000W, Q = 10000Var, where P is active power and Q is reactive power. The dotted line represents the communication link between the GFCs. Each GFC only exchanges information with the GFC connected to the communication link. The specific parameters in the AC microgrid system are shown in the following table. Each GFC has a different equivalent output impedance.

[0042] Table 1 Specific parameters in 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 respectively, obtains its own frequency, voltage effective value, active power and reactive power through calculation, and communicates with neighboring nodes in the sparse communication network to obtain the active power and reactive power of neighboring nodes. After this process, its own frequency, voltage effective value, active power and reactive power, as well as the active power and reactive power of neighboring nodes are obtained, which will be used for the proposed multi-grid inverter parallel control strategy;

[0045] S3: On the basis of VSG control, active support control of frequency and voltage and coordinated control of active and reactive power are added to construct a grid-type converter control strategy combining active support and coordinated control. Based on the acquired node frequency, voltage effective value, active power and reactive power, as well as the active and reactive power of neighboring nodes, the grid-type converter control strategy combining active support and coordinated control is used to calculate 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, and the output voltage target value of each grid-type converter is adjusted through virtual impedance control and voltage loop and current loop control.

[0046] In the traditional method, VSG control is implemented on the grid-connected converter, and virtual impedance control is used to improve its power distribution capability;

[0047] VSG control is a kind of grid-type control. It controls the frequency and voltage effective value of the grid-type converter (GFC) to maintain the bus frequency and voltage of the AC microgrid system and realize the reasonable distribution of power among different grid-type converters (GFC). It includes two parts: active-frequency control and reactive-voltage control.

[0048] VSG performs active power-frequency control by simulating the rotor motion equation of the synchronous generator, which is as follows:

[0049]

[0050] Where ω is the VSG angular frequency, ω n is the rated angular frequency, J is the moment of inertia, D is the damping coefficient, P m is the active power reference value, P is the active power output by VSG, P ref is the rated value of active power, K ω is the active angular frequency droop coefficient, t is the 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 reasonable distribution of active power by controlling the frequency of each grid-type converter (GFC), but it will cause the frequency to deviate from the rated value;

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

[0053]

[0054] In the formula, Q m is the reactive power reference value, Q ref is the reactive power rating, Q is the reactive power output by VSG, and U n is the voltage rating, U is the output voltage of VSG, E d is the d-axis component of the voltage command value, K v is the reactive voltage droop coefficient, K is the integral coefficient, is the integral symbol;

[0055] When VSG is in steady state, Q = Q m =Q ref +K v (U n -U), similar to active power-frequency control, while distributing reactive power, it will cause the output voltage of the grid-connected converter (GFC) to deviate from the rated value;

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

[0057] In VSG control, virtual impedance is often used to mitigate the impact of the difference in output impedance of different grid-connected converters (GFCs). Appropriate virtual impedance can decouple active power from reactive power and improve power distribution. The expression of virtual impedance control is as follows:

[0058]

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

[0060] In order to avoid voltage and current fluctuations, the output voltage and current of the grid-connected converter (GFC) are usually controlled using a voltage loop and a current loop:

[0061]

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

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

[0064] The VSG-controlled grid-type converter adjusts active and reactive power by changing frequency and voltage, but this adjustment method will cause the frequency and voltage of the grid-type converter to deviate from the rated value, reducing the power quality. To solve this problem, it is necessary to actively support the frequency and voltage of the grid-type converter.

[0065] The active support of the frequency and voltage of the grid-connected converter is achieved by adding active frequency and voltage support items in the VSG control. This support item will change the steady-state state of the VSG control to achieve the purpose of returning the frequency and voltage to the rated value. The relationship between the added VSG frequency and active power can be expressed as follows:

[0066]

[0067] In the formula, ω v is the frequency command value of VSG control, e ω is the frequency adjustment term, α is the frequency active support coefficient;

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

[0069]

[0070] In the formula, E v is the voltage command value of VSG control, e U is the voltage adjustment term, β is the voltage active support coefficient;

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

[0072]

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

[0074] Based on sparse communication networks and multi-agent consistency theory, each GFC exchanges power information of other GFCs required for the collaborative control strategy, and performs collaborative control of active and reactive power to achieve accurate distribution of active and reactive power among GFCs.

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

[0076] For a sparse communication network with n nodes, if there is a communication link ij connecting GFC i and GFCj , then GFC j is considered to be in the neighborhood set N i In the above example, j∈N i , GFC i Only from the communication coefficient a ij = 1 neighborhood set N i Receive information in, otherwise a ij = 0. The symmetric n×n order adjacency equation A = (a ij ) n×n Indicates that GFC i is the i-th grid-connected converter, GFC j is the jth grid-type converter, i and j are the numbers of the grid-type converter;

[0077] Define the weights between GFCs:

[0078]

[0079] Among them, d ij For GFC i With GFC j The weight between

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

[0081]

[0082] Among them, l ij are the off-diagonal elements of the Laplacian matrix, l ii are diagonal elements;

[0083] The present invention adopts a consistency algorithm to design the interaction of adjacent information. The consistency variable x of each node i The consistency variable x of any adjacent node is adjusted according to the consistency variable of its neighboring nodes. As the number of iterations gradually increases, the consistency variable x of any adjacent node i 、x j tend to be consistent, satisfying |x i (k)-x j (k)|→0, when the state variables of all nodes reach consistency within the convergence condition range, the AC microgrid system converges. The first-order consistency algorithm is described as:

[0084]

[0085] In the formula, x i is a consistency variable, i=1,2,…,n, is the consistency variable x i The differential of

[0086] The control strategy proposed in the present invention takes frequency, voltage, active power and reactive power as adjustment targets. Since the adjustment targets of frequency and voltage are only related to the rated value and can be completed without information interaction, only the active and reactive power of the GFC can be used as the adjustment target. Based on the local state variables of the GFC and the state variables of the adjacent GFCs, the coordinated control of the state quantities of each GFC is achieved through a consistency algorithm.

[0087] It can be seen that after adding the frequency and voltage active support items, the original Pf droop relationship of the VSG is destroyed, and the VSG control will no longer be able to achieve a reasonable distribution of active power. In addition, for the island system, the precise distribution of reactive power requires a certain difference in the voltage of each grid-type converter (GFC), which is inconsistent with controlling the voltage of all grid-type converters (GFC) to the rated value. Therefore, the aforementioned frequency and voltage active support method must be improved so that the active and reactive power can be distributed according to the expected target without affecting the frequency and voltage active support functions.

[0088] According to the multi-agent consensus theory, the following consensus algorithm can achieve the goal of evenly distributing active and reactive power among the GFCs:

[0089]

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

[0091] However, the grid-type converter cannot directly control the active and reactive power. For a multi-grid-type converter parallel system whose line impedance is approximately pure inductive, the purpose of changing its own active and reactive power is generally achieved by controlling the frequency to change its own phase and controlling the voltage command value to change its own output voltage. Therefore, the consistency algorithm with the goal of evenly distributing active and reactive power is rewritten as:

[0092]

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

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

[0095]

[0096] Among them, ω vi For GFC i The frequency command value of VSG control, e ωi For GFC i The frequency adjustment term, P mi For GFC i Active power reference value, P refi For GFC i Rated value of active power, K ωi For GFC i Active angular frequency droop coefficient, α i For GFC i The frequency active support coefficient of

[0097] At this time, the frequency and active power steady-state values ​​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 according to the expected target;

[0100] Since the precise distribution of reactive power requires a certain voltage difference between each grid-type converter (GFC), which conflicts with the voltage control of all grid-type converters (GFC) to the rated value, it is necessary to select a leader from all grid-type converters (GFC), and only actively support the voltage of the grid-type converter (GFC) selected as the leader, and at the same time, all grid-type converters (GFC) are coordinated to control reactive power. The expression is as follows:

[0101]

[0102] At this time, the voltage and reactive power of each grid-connected converter (GFC) in steady state will meet the following requirements:

[0103]

[0104] Where U leader is the selected voltage that actively supports the output voltage of the leader;

[0105] The present invention is aimed at the scenario of multiple machines in parallel operation of grid-type converters. On the basis of VSG control, it implements active frequency and voltage support and a power collaborative control method based on a sparse communication network, which makes up for the defects of VSG control, realizes the error-free recovery of the frequency and voltage of the converter and the precise allocation of active and reactive power, and achieves the best control effect.

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

[0107] Figure 5 The simulation results show four processes under the single bus topology, namely: Figure 5 (a), at t = 2s, frequency active support control is added on the basis of general VSG control, and the frequency of each GFC is controlled to the rated value; Figure 5 (b) Before t = 8s, due to the influence of active frequency support control, the active power of each GFC is no longer reasonably distributed. At t = 8s, active power coordinated control is added to redistribute the active power of each GFC correctly; Figure 5 (c), at t = 15s, reactive power cooperative control is added. Relying solely on VSG control cannot accurately distribute reactive power according to the expected target, so there is a deviation. When reactive power cooperative control is added, this deviation is eliminated; Figure 5 (d) At t = 20s, active support for the voltage of the leader is added, and the leader voltage is controlled to the rated value.

[0108] Figure 6 To adopt Figure 4 The simulation results of the mesh topology are shown below: Figure 6 (a), at t = 2s, frequency active support control is added on the basis of general VSG control, and the frequency of each GFC is controlled to the rated value; Figure 6 (b), at t = 8s, active power coordinated control is added, and the active power of each GFC is correctly redistributed; Figure 6 (c), at t = 15s, reactive power cooperative control is added and reactive power is accurately distributed; Figure 6 (d) At t = 20s, active support for the voltage of the leader is added, and the leader voltage is controlled to the rated value.

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

[0110] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A method for controlling the parallel operation of multiple machines of a grid-connected energy storage converter, characterized in that: The following steps are involved: S1. For an AC microgrid system including a meshed converter, a sparse communication network is established for realizing information interaction between different meshed 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 respectively, obtains its own frequency, voltage RMS, active power and reactive power through calculation, and communicates with neighboring nodes in the sparse communication network to obtain the active power and reactive power of neighboring nodes; S3: On the basis of VSG control, active support control of frequency and voltage and coordinated control of active and reactive power are added to construct a grid-type converter control strategy combining active support and coordinated control. Based on the acquired node frequency, voltage effective value, active power and reactive power, as well as the active and reactive power of neighboring nodes, the grid-type converter control strategy combining active support and coordinated control is used to calculate 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, and the output voltage target value of each grid-type converter is adjusted through virtual impedance control and voltage loop and current loop control. S4: The voltage target value and output frequency obtained by the grid-type converter control strategy combining active support and collaborative control are converted into a three-phase AC voltage waveform through dq transformation, which is further modulated into a three-phase PWM switch control signal and applied to the grid-type converter to achieve the control effect.

2. A 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 meshed converter is regarded as a node, and if there is a communication connection between two nodes, they are called adjacent or neighbor nodes.

3. The method for controlling the parallel operation of multiple machines of a grid-connected energy storage converter according to claim 1, characterized in that: The grid-type converter control strategy combining active support and collaborative control described in S3 includes: actively supporting the frequency of all grid-type converters and collaboratively controlling the active power; selecting a leader from all grid-type converters, and only actively supporting the voltage of the grid-type converter selected as the leader, while collaboratively controlling the reactive power of all grid-type converters.

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

5. The method for controlling the parallel operation of multiple machines of a grid-type energy storage converter according to claim 3 is characterized in that: The expression for selecting a leader from all grid-type converters, actively supporting voltage only for the grid-type converter selected as the leader, and performing coordinated reactive power control on all grid-type converters is: Among them, Q m is the reactive power reference value, Q ref is the reactive power rating, Q is the reactive power output by VSG, and U n is the voltage rating, U is the output voltage of VSG, E d is the d-axis component of the voltage command value, K v is the reactive voltage droop coefficient, K is the integral coefficient, is the integral symbol; E v is the voltage command value of VSG control, e U is the voltage adjustment term, β is the voltage active support coefficient; Q i For GFC i Reactive power, Q j For GFC j of reactive power.

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

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

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