A distributed control method for hybrid network-constructed energy storage converter

Abstract

This invention discloses a distributed control method for hybrid grid-connected energy storage converters, relating to the field of electrical engineering. This invention addresses two power sources connected to the power system via a grid-connected converter: supercapacitors and batteries. Based on a distributed control strategy for hybrid energy storage using multi-agent theory, a power control target for the grid-connected converter that meets the requirements of hybrid energy storage is obtained. Then, VSG control and virtual impedance control are used to ensure that the power output of the supercapacitors and batteries conforms to the obtained power control target. This achieves hybrid energy storage across multiple distributed supercapacitors and batteries without requiring modifications or additions to electrical equipment. The power can be directly applied to the energy storage power source connected to the AC grid via the grid-connected converter. The proposed hybrid energy storage control strategy for grid-connected converters allows supercapacitors and batteries to handle the high-frequency and low-frequency components of the power output, respectively. Simultaneously, a sparse communication network is used for information exchange, reducing communication burden.

Description

Technical Field

[0001] This invention relates to the field of electrical engineering, and more specifically to a distributed control method for hybrid grid-connected energy storage converters. Background Technology

[0002] Hybrid energy storage systems combine different types of energy storage technologies, such as lithium-ion batteries and supercapacitors. When power changes, the supercapacitor, which can rapidly release energy, is activated first to quickly respond to power demands. Then, the power output of the lithium-ion battery is changed relatively slowly, gradually replacing the supercapacitor and providing stable power output over a long period. Through this process, hybrid energy storage systems allow these two types of energy storage technologies to complement each other and leverage their respective advantages.

[0003] Traditional hybrid energy storage control methods involve installing DC-DC converters on the DC bus to control the output power of both batteries and supercapacitors, thereby achieving hybrid energy storage. This method relies on the DC bus and cannot be directly applied to distributed energy storage power sources connected to AC microgrids via grid-connected converters. Therefore, it is necessary to explore new hybrid energy storage implementation methods, starting with the control methods of grid-connected converters.

[0004] In the control of grid-connected converters, VSG control is a widely used method. It enables the converter to simulate the operation of a synchronous generator rotor and controls the power distribution based on rated power and droop coefficient. VSG control can stabilize the frequency of grid-connected converters. However, the power distribution required for hybrid energy storage is more complex, so VSG control cannot be directly used in the implementation of hybrid energy storage. Furthermore, for grid-connected converters composed of power electronic devices, simply mimicking the characteristics of a synchronous generator set does not fully realize its capabilities. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a distributed control method for hybrid grid-connected energy storage converters. For both supercapacitors and batteries connected to the power system via grid-connected converters, a distributed control strategy based on multi-agent theory is used to obtain a power control target for the grid-connected converter that meets the requirements of hybrid energy storage. Then, VSG control and virtual impedance control are applied to ensure that the power output of the supercapacitors and batteries conforms to the obtained power control target, thereby achieving hybrid energy storage in multiple distributed supercapacitors and batteries.

[0006] A distributed control method for hybrid grid-connected energy storage converters includes the following steps:

[0007] S1. For an AC microgrid system including supercapacitors, batteries, and grid-type converters for controlling supercapacitors and batteries, establish a sparse communication network to realize information interaction between different grid-type converters in the AC microgrid system.

[0008] Furthermore, 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.

[0009] Furthermore, the information includes active power;

[0010] Furthermore, the grid-type converter includes two types: a first type of grid-type converter and a second type of grid-type converter. The first type of grid-type converter is a grid-type converter connected to a supercapacitor, and the second type of grid-type converter is a grid-type converter connected to a battery.

[0011] S2: Based on the established sparse communication network, each node measures its own three-phase output voltage and output current, calculates its own active power, and communicates with neighboring nodes in the sparse communication network to obtain the active power of neighboring nodes.

[0012] S3: Construct a hybrid energy storage distributed control strategy based on multi-agent theory. Each grid-type converter implements the hybrid energy storage distributed control strategy according to the active power of its neighboring nodes and its own type, and determines its own power control target.

[0013] The power control objective is:

[0014]

[0015] In the formula, P tari Let M be the power control target for the i-th grid-type converter, where α and β are coefficients for the two communication methods, and the sum of α and β is 1. i With N i Let k represent the neighborhood set of the same type of network converter that has a communication connection with the i-th network converter, and the neighborhood set of different types of network converters that have a communication connection with the i-th network converter, respectively; c Let k be a coefficient representing the type of the i-th grid-type converter. If the i-th grid-type converter is a type I grid-type converter, then k c =1 otherwise =0; T is the low-pass filter time constant, s is a complex variable, P i P is the active power output of the power supply connected to the i-th grid-type converter. j The active power output of the power supply connected to the j-th grid-type converter;

[0016] S4: Construct a hybrid energy storage control strategy for grid-connected converters that combines VSG control and virtual impedance control. Each grid-connected converter uses the hybrid energy storage control strategy to execute the power control target and obtain the effective voltage value and output frequency required to achieve hybrid energy storage.

[0017] The hybrid energy storage control strategy for grid-connected converters that combines VSG control and virtual impedance control includes:

[0018] VSG control:

[0019]

[0020] Where, ω i Let ω be the angular frequency of the i-th grid-type converter. vi e is the frequency command value for the VSG control of the i-th grid-type converter. ωi For the frequency adjustment term of the i-th grid-type converter, P mi P is the active power setpoint for the VSG control of the i-th grid-type converter. refi K is the active power reference value for the droop control of the i-th grid-type converter. ω Frequency adjustment factor;

[0021] Virtual impedance control:

[0022]

[0023] In the formula, u odi * For the virtual impedance control of the i-th grid converter, the output on the d-axis is u. oqi * E is the output of the virtual impedance control on the q-axis for the i-th grid converter. di E represents the d-axis component of the voltage command value for the i-th grid-type converter. qi Let i be the q-axis component of the voltage command value of the i-th grid-type converter. odi The d-axis component of the VSG output current of the i-th grid-type converter, i oqi Let r be the q-axis component of the VSG output current of the i-th grid-type converter. v and L v These are virtual resistance and inductance, respectively;

[0024] Furthermore, in virtual impedance control, if the grid-connected converter is a type I grid-connected converter, then the virtual inductance of this grid-connected converter is L. vC If the grid-connected converter is of type II grid-connected converter, then the virtual inductance of this grid-connected converter is L. vB :

[0025] L vB =L vC +L h

[0026] Among them, L vB The virtual impedance L of a grid-type converter that uses a battery as a DC source vC The virtual impedance L of a grid-type converter that uses a supercapacitor as a DC source h It is an additional virtual impedance added to achieve hybrid energy storage;

[0027] S5: The obtained effective voltage value and output frequency 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.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention proposes a distributed control method for hybrid grid-connected energy storage converters. This method does not require modification or addition of power equipment and can be directly applied to common energy storage power sources connected to the AC grid through grid-connected converters.

[0030] 2. This invention proposes a hybrid energy storage control strategy for grid-type converters that combines VSG control and virtual impedance control. This method enables supercapacitors and batteries to respectively handle the high-frequency and low-frequency components of power output, giving full play to their respective advantages.

[0031] 3. This invention draws on the multi-agent consensus theory and proposes a hybrid energy storage distributed control strategy based on the multi-agent theory, which enables multiple distributed energy storage power sources to reasonably divide their work and jointly form hybrid energy storage. At the same time, a sparse communication network is used for information exchange, which reduces the communication burden. Attached Figure Description

[0032] Figure 1 This is a block diagram of the VSG control after adding a frequency adjustment term in an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of a distributed control method for a hybrid grid-connected energy storage converter according to an embodiment of the present invention. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] like Figure 1 and Figure 2 As shown, a distributed control method for hybrid grid-connected energy storage converters includes the following steps:

[0036] S1. For an AC microgrid system including supercapacitors, batteries, and grid-type converters for controlling the supercapacitors and batteries, a sparse communication network is established to realize information exchange between different grid-type converters in the AC microgrid system; 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; the information includes active power;

[0037] The grid-type converter includes two types: the first type of grid-type converter and the second type of grid-type converter. The first type of grid-type converter is a grid-type converter connected to a supercapacitor, and the second type of grid-type converter is a grid-type converter connected to a battery. The control strategies used in subsequent control will differ for different types of grid-type converters.

[0038] S2: Based on the established sparse communication network, each node measures its own three-phase output voltage and output current, calculates its own active power, and communicates with neighboring nodes in the sparse communication network to obtain the active power of neighboring nodes.

[0039] S3: Construct a hybrid energy storage distributed control strategy based on multi-agent theory. Each grid-type converter implements the hybrid energy storage distributed control strategy according to the active power of its neighboring nodes and its own type (first-type grid-type converter and second-type grid-type converter) to determine its own power control target.

[0040] For distributed network converters, it is necessary to consider communication methods and how to implement coordinated control based on the information obtained from communication to ensure that all network converters output power correctly. In this regard, multi-agent systems are a good choice.

[0041] 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 that utilize sparse communication networks to enable each agent to exchange local information and execute adjustment strategies, ultimately achieving consistent behavior or state throughout the system.

[0042] In a multi-agent system, if there exists a transmission line ij connecting the i-th grid-type converter GFC... i and the j-th grid-type converter GFC j Then it is called GFC j In the neighborhood set N i In the above, j∈N is represented as i GFCi can only accept data from N. i Information about other GFC (grid-type converters) is then used to adjust the consistency variable x based on the obtained information.i The consistency variable x of any adjacent nodes. i and x j The convergence of state variables across all nodes until they reach a consensus is called system convergence. The first-order consensus algorithm is described as follows:

[0043]

[0044] In the formula, For the consistency variable x i The derivative, i = 1, 2, ..., n, where n is the total number of grid-type converters in the AC microgrid system, d ij This is a consistency control coefficient, which is generally related to communication weight.

[0045] In the problem of hybrid energy storage, although the control objectives of supercapacitors and batteries are not the same, the idea of ​​multiple agents interacting with each other and executing their own strategies remains important.

[0046] In the designed multi-agent system for hybrid energy storage, communication between different types of grid-connected converters is crucial. First-type and second-type grid-connected converters communicate to distribute high-frequency and low-frequency power, thus achieving the power control target of the hybrid energy storage system. For grid-connected converters of the same type, such as two first-type or two second-type grid-connected converters, communication controls their power output to achieve consistency. A grid-connected converter may be connected to both its own and different types of grid-connected converters, and will be affected by both. The power control target P for each grid-connected converter used to control the power output is obtained in this way. tar As shown in the following formula:

[0047]

[0048] In the formula, P tari Let M be the power control target for the i-th grid-type converter, where α and β are coefficients for the two communication methods, and the sum of α and β is 1. i With N i Let k represent the neighborhood set of the same type of network converter that has a communication connection with the i-th network converter, and the neighborhood set of different types of network converters that have a communication connection with the i-th network converter, respectively; c Let k be a coefficient representing the type of the i-th grid-type converter. If the i-th grid-type converter is a type I grid-type converter, then k c =1 otherwise =0; T is the low-pass filter time constant, s is a complex variable, P i P is the active power output of the power supply connected to the i-th grid-type converter. jThe active power output of the power supply connected to the j-th grid-type converter;

[0049] In this way, the P values ​​of each grid-type converter can be obtained. tar Then, it is applied to the subsequent grid-type converter control formula for power regulation.

[0050] In this way, in the communication between adjacent first-type grid converters and second-type grid converters, the power of high frequency and low frequency is rationally allocated, while the communication between grid converters of the same type makes their power tend to be consistent, producing a transmission effect, and ultimately realizing the hybrid energy storage of multiple supercapacitors and batteries.

[0051] S4: Construct a hybrid energy storage control strategy for grid-connected converters that combines VSG control and virtual impedance control. Each grid-connected converter uses the hybrid energy storage control strategy to execute the power control target and obtain the effective voltage value and output frequency required to achieve hybrid energy storage.

[0052] The hybrid energy storage control strategy combining VSG control and virtual impedance control for grid-type converters precisely and stably controls the power output of the grid-type converter by adding a frequency adjustment term to the traditional VSG control. Simultaneously, virtual impedance control is used to control the power variation of the second type of grid-type converter under load changes by applying a larger virtual inductance compared to the first type. Through these two control methods (VSG control and virtual impedance control), the supercapacitor and battery are rationally allocated power under the control of the grid-type converter, achieving the goal of hybrid energy storage where the supercapacitor handles high-frequency power and the battery handles low-frequency power.

[0053] Hybrid energy storage systems need to consider the energy storage characteristics of each component and determine their respective power target values ​​in real time to achieve a reasonable and efficient allocation of power between battery energy storage and supercapacitor energy storage.

[0054] Unlike hybrid energy storage in DC microgrid systems, power distribution in AC microgrid systems cannot be achieved by adjusting DC / DC circuits. To ensure that supercapacitors and batteries reach their respective power target values, it is necessary to discuss the control and power regulation methods of grid-type converters.

[0055] VSG-controlled grid-connected converters can provide inertial support for AC microgrid systems, are friendly to AC microgrid system operation, and are widely used. Therefore, this paper discusses hybrid energy storage based on VSG control. The active-frequency control loop of a traditional VSG-controlled grid-connected converter is shown below:

[0056]

[0057] Where 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 setpoint for VSG control. ref K is the active power reference value for droop control. ω The active angular frequency droop coefficient is t, where t is time.

[0058] Normally, the active-frequency control loop of the VSG will distribute the active power of each grid-type converter according to the droop characteristic, resulting in P=P m =P ref +K ω (ω n The result of -ω). Based on VSG control, adding an additional adjustment term to the frequency can change the active power allocation result, making it any reasonable allocation target;

[0059]

[0060] Where, ω i Let ω be the angular frequency of the i-th grid-type converter. vi e is the frequency command value for the VSG control of the i-th grid-type converter. ωi For the frequency adjustment term of the i-th grid-type converter, P mi P is the active power setpoint for the VSG control of the i-th grid-type converter. refi K is the active power reference value for the droop control of the i-th grid-type converter. ω Frequency adjustment factor;

[0061] This approach achieves the goal of allocating the low-frequency component of the total power to the battery, which is required by hybrid energy storage. However, since the impact of frequency regulation on power output is relatively slow, frequency regulation alone cannot effectively allocate the high-frequency component when the AC microgrid system loads a rapid power increase.

[0062] For grid-connected converters in isolated AC microgrid systems, since they always output three-phase AC power close to their rated voltage and frequency, when the load in the AC microgrid system changes, these second-type grid-connected converters will immediately take over the power. This contradicts the goal of hybrid energy storage, which only allows supercapacitors to handle high-frequency components. For grid-connected converters, the dynamic characteristics of active power are affected by the power supply output impedance; power supplies with higher output impedance will take over less power changes when the load changes.

[0063] Therefore, applying virtual impedance control to the control of in-grid converters, by introducing a simulated impedance into the control calculations, can mimic the actual impedance in terms of the external characteristics of the power source. This is commonly used to improve the stability of AC microgrid systems and optimize power distribution.

[0064]

[0065] In the formula, u odi * For the virtual impedance control of the i-th grid converter, the output on the d-axis is u. oqi * E is the output of the virtual impedance control on the q-axis for the i-th grid converter. di E represents the d-axis component of the voltage command value for the i-th grid-type converter. qi Let i be the q-axis component of the voltage command value of the i-th grid-type converter. odi The d-axis component of the VSG output current of the i-th grid-type converter, i oqi Let r be the q-axis component of the VSG output current of the i-th grid-type converter. v and L v These are virtual resistance and inductance, respectively;

[0066] When virtual impedance is used to compensate for differences in actual impedance, it can make the power response of different converters more consistent when facing load changes. Conversely, if the output impedance of the battery is increased by virtual impedance, especially the virtual inductance which has a greater impact on power changes, the distribution of power between the battery and the supercapacitor can be controlled, so that the supercapacitor bears more power when the load changes. This change is in line with the goal of making the supercapacitor bear the high-frequency components of power in hybrid energy storage.

[0067] L vB =L vC +L h

[0068] Among them, L vB The virtual impedance L of a grid-type converter that uses a battery as a DC source vC The virtual impedance L of a grid-type converter that uses a supercapacitor as a DC source h It is an additional virtual impedance added to achieve hybrid energy storage;

[0069] By applying the power control method combining VSG control and virtual impedance control to a grid-type converter, the supercapacitor and battery controlled by the grid-type converter can be configured to distribute power according to the requirements of hybrid energy storage.

[0070] S5: The obtained effective voltage value and output frequency 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.

[0071] 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 distributed control method for hybrid grid-connected energy storage converters, characterized in that, Includes the following steps: S1. For an AC microgrid system including supercapacitors, batteries, and grid-type converters for controlling supercapacitors and batteries, establish a sparse communication network to realize information interaction 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 active power, and communicates with neighboring nodes in the sparse communication network to obtain the active power of neighboring nodes. S3: Construct a hybrid energy storage distributed control strategy based on multi-agent theory. Each grid-type converter implements the hybrid energy storage distributed control strategy according to the active power of its neighboring nodes and its own type, and determines its own power control target. S4: Construct a hybrid energy storage control strategy for grid-connected converters that combines VSG control and virtual impedance control. Each grid-connected converter uses the hybrid energy storage control strategy to execute the power control target and obtain the effective voltage value and output frequency required to achieve hybrid energy storage. S5: The obtained effective voltage value and output frequency are converted 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 distributed control method for hybrid grid-connected energy storage converters according to claim 1, characterized in that, In the sparse communication network described in S1, 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.

3. The distributed control method for hybrid grid-connected energy storage converters according to claim 1, characterized in that, The information described in S1 includes active power.

4. The distributed control method for hybrid grid-connected energy storage converters according to claim 1, characterized in that, The grid-type converter includes two types: a first type grid-type converter and a second type grid-type converter. The first type grid-type converter is a grid-type converter connected to a supercapacitor, and the second type grid-type converter is a grid-type converter connected to a battery.

5. The distributed control method for hybrid grid-connected energy storage converters according to claim 4, characterized in that, The power control objective described in S3 is: In the formula, P tari Let M be the power control target for the i-th grid-type converter, where α and β are coefficients for the two communication methods, and the sum of α and β is 1. i With N i Let k represent the neighborhood set of the same type of network converter that has a communication connection with the i-th network converter, and the neighborhood set of different types of network converters that have a communication connection with the i-th network converter, respectively; c Let k be a coefficient representing the type of the i-th grid-type converter. If the i-th grid-type converter is a type I grid-type converter, then k c =1 otherwise =0; T is the low-pass filter time constant, s is a complex variable, P i P is the active power output of the power supply connected to the i-th grid-type converter. j The active power output of the power supply connected to the j-th grid-type converter.

6. The distributed control method for hybrid grid-connected energy storage converters according to claim 4, characterized in that, The hybrid energy storage control strategy for grid-connected converters that combines VSG control and virtual impedance control, as described in S4, includes: VSG control: Where, ω i Let ω be the angular frequency of the i-th grid-type converter. vi e is the frequency command value for the VSG control of the i-th grid-type converter. ωi For the frequency adjustment term of the i-th grid-type converter, P mi P is the active power setpoint for the VSG control of the i-th grid-type converter. refi K is the active power reference value for the droop control of the i-th grid-type converter. ω Frequency adjustment factor; Virtual impedance control: In the formula, u odi * For the virtual impedance control of the i-th grid converter, the output on the d-axis is u. oqi * E is the output of the virtual impedance control on the q-axis for the i-th grid converter. di E represents the d-axis component of the voltage command value for the i-th grid-type converter. qi Let i be the q-axis component of the voltage command value of the i-th grid-type converter. odi The d-axis component of the VSG output current of the i-th grid-type converter, i oqi Let r be the q-axis component of the VSG output current of the i-th grid-type converter. v and L v These are virtual resistance and inductance, respectively.

7. The distributed control method for hybrid grid-connected energy storage converters according to claim 6, characterized in that, In the virtual impedance control, if the grid-connected converter is a type I grid-connected converter, then the virtual inductance of the grid-connected converter is L. vC If the grid-connected converter is of type II grid-connected converter, then the virtual inductance of this grid-connected converter is L. vB : L vB =L vC +L h Among them, L vB The virtual impedance L of a grid-type converter that uses a battery as a DC source vC The virtual impedance L of a grid-type converter that uses a supercapacitor as a DC source h It is an additional virtual impedance added to achieve hybrid energy storage.

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