Distributed control method for hybrid network construction energy storage converter

Abstract

The invention discloses a distributed control method for a hybrid network construction energy storage converter, and relates to the field of electrical engineering. The method comprises the following steps: aiming at two power supplies of a super capacitor and a storage battery which are accessed to a power system through a network construction type converter, obtaining a network construction type converter power control target which meets the hybrid energy storage requirement according to a hybrid energy storage distributed control strategy based on a multi-agent theory, and then applying VSG control and virtual impedance control to realize hybrid energy storage control. The power output of the super-capacitors and the storage battery accords with the obtained power control target, so that hybrid energy storage is realized in the distributed super-capacitors and the storage battery, electric power equipment does not need to be transformed or additionally arranged, and the hybrid energy storage can be directly applied to an energy storage power supply connected to an alternating current power grid through a network-forming converter; according to the provided hybrid energy storage control strategy of the network construction type converter, the super capacitor and the storage battery can respectively bear high-frequency and low-frequency components of power output, and meanwhile, a sparse communication network is adopted for information exchange, so that the communication burden is reduced.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering, and in particular to a distributed control method for a hybrid grid-connected energy storage converter. Background Art

[0002] The hybrid energy storage system uses different types of energy storage technologies, such as lithium-ion batteries and supercapacitors. When the power changes, the supercapacitor that can quickly release energy is activated first to quickly respond to the power demand, and then the power output of the lithium-ion battery is changed relatively slowly, gradually replacing the supercapacitor and then outputting electrical energy stably for a long time. Through this process, the hybrid energy storage system can make the two types of energy storage technologies complement each other and give full play to their respective advantages.

[0003] The traditional hybrid energy storage control method is to achieve hybrid energy storage by adding a DC-DC converter to the battery and supercapacitor on the DC bus to control the output power of both. This method relies on the DC bus and cannot be directly applied to distributed energy storage power sources connected to the AC microgrid through a grid-type converter. Therefore, it is necessary to start with the control method of the grid-type converter and find a new hybrid energy storage implementation method.

[0004] In the control of grid-type converters, VSG control is a widely used control method, which enables the converter to simulate the working process of the synchronous generator rotor and control the power distribution of the power supply according to the rated power and droop coefficient. VSG control can stabilize the frequency of the grid-type converter, but the power distribution required by hybrid energy storage is more complicated, so VSG control cannot be directly used in the realization of hybrid energy storage. At the same time, for the grid-type converter composed of power electronic devices, simply imitating the characteristics of the synchronous generator set to operate cannot reflect its full functions. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a distributed control method for hybrid grid-connected energy storage inverters. For the two power sources of supercapacitors and batteries connected to the power system through grid-connected inverters, according to the hybrid energy storage distributed control strategy based on multi-agent theory, the power control target of the grid-connected inverter that meets the hybrid energy storage needs is obtained. Then, VSG control and virtual impedance control are used to make the power output of supercapacitors and batteries meet the obtained power control target, thereby realizing hybrid energy storage in multiple distributed supercapacitors and batteries.

[0006] A distributed control method for a hybrid grid-connected energy storage converter comprises the following steps:

[0007] S1. For an AC microgrid system including a supercapacitor, a battery, and a grid-type converter for controlling the supercapacitor and the battery, a sparse communication network is established for realizing information interaction between different grid-type converters in the AC microgrid system;

[0008] Furthermore, 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;

[0009] Further, the information includes active power;

[0010] Furthermore, the grid-type converter includes two types, namely a first type of grid-type converter and a second type of grid-type converter, wherein 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 respectively, obtains its own active power through calculation, 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-connected converter implements the hybrid energy storage distributed control strategy according to the active power of neighboring nodes and its own type, and determines its own power control target.

[0013] The power control target is:

[0014]

[0015] Where P tari is the power control target of the i-th grid-connected converter, α and β are the coefficients of the two communications, and the sum of α and β is 1, M i With N i k respectively represent the neighborhood set consisting of the same type of meshed converters that have communication connection with the i-th meshed converter and the neighborhood set consisting of different types of meshed converters that have communication connection with the i-th meshed converter; c is the coefficient of the type of the i-th grid-type converter. If the i-th grid-type converter is a first-type grid-type converter, then k c is 1, otherwise it is 0; T is the low-pass filter time constant, s is a complex variable, P i is the active power output of the power source connected to the i-th grid-connected converter, P j is the active power output of the power source connected to the jth grid-connected converter;

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

[0017] The hybrid energy storage control strategy of the grid-connected converter combining VSG control and virtual impedance control includes:

[0018] VSG Control:

[0019]

[0020] Among them, ω i is the angular frequency of the i-th grid-connected converter, ω vi is the frequency command value of the VSG control of the i-th grid-connected converter, e ωi is the frequency adjustment item of the i-th grid-connected converter, P mi is the active power setting value of the VSG control of the i-th grid-connected converter, P refi is the active power reference value of the droop control of the i-th grid-connected converter, K ω Frequency adjustment factor;

[0021] Virtual Impedance Control:

[0022]

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

[0024] Furthermore, in the virtual impedance control, if the type of the grid-type converter is the first type grid-type converter, the virtual inductance of the grid-type converter is L vC If the type of the grid-type converter is the second type grid-type converter, the virtual inductance of the grid-type converter is L vB :

[0025] L vB =L vC +L h

[0026] Among them, L vB is the virtual impedance of the grid-connected converter with the battery as the DC source, L vC is the virtual impedance of the grid-connected converter with supercapacitor as the DC source, L h It is the additional virtual impedance added to realize hybrid energy storage;

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

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

[0029] 1. The present invention proposes a distributed control method for a hybrid grid-connected energy storage converter. This method does not require modification or additional installation of power equipment and can be directly applied to a common energy storage power source connected to an AC power grid through a grid-connected converter.

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

[0031] 3. The present invention draws on the multi-agent consistency theory and proposes a hybrid energy storage distributed control strategy based on the multi-agent theory, so that multiple distributed energy storage power sources can be reasonably divided into two groups to form a hybrid energy storage. At the same time, a sparse communication network is used for information exchange to reduce the communication burden. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0033] Figure 2 It is a schematic diagram of a distributed control method for a hybrid grid energy storage converter in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

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

[0036] S1. For an AC microgrid system including a supercapacitor, a battery and a meshed converter for controlling the supercapacitor and the battery, a sparse communication network is established for realizing information interaction between different meshed converters in the AC microgrid system; 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; the information includes active power;

[0037] The grid-type converter includes two types, namely, 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. Different types of grid-type converters have different control strategies used in subsequent control.

[0038] S2: Based on the established sparse communication network, each node measures its own three-phase output voltage and output current respectively, obtains its own active power through calculation, 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 the 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 multiple distributed grid-type converters, it is necessary to consider the communication method and how to implement coordinated control based on the information obtained from the communication so that all grid-type converters can output power correctly. In this regard, multi-agent is a good choice.

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

[0042] In a multi-agent system, if there is a transmission line ij connecting the i-th grid-connected converter GFC i and the jth grid-connected converter GFC j , then it is called GFC j In the neighborhood set N i In the example, j∈N i GFCi can only accept i The information of other GFCs (grid-connected converters) is then used to adjust its own consistency variable x according to the information obtained.i , so that the consistency variable x of any adjacent node i and x j The convergence of the state variables of all nodes is called system convergence. The first-order consistency algorithm is described as:

[0043]

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

[0045] In the problem of hybrid energy storage, although the control objectives of supercapacitors and batteries are not consistent, the idea of ​​multiple agents exchanging information with their neighbors and executing their own strategies is still important.

[0046] In the designed hybrid energy storage multi-agent system, for the communication between different types of grid-type converters, the first type of grid-type converter and the second type of grid-type converter use communication to distribute high-frequency and low-frequency power, thereby achieving the power control target of the hybrid energy storage; and for the same type of grid-type converters, such as two first type of grid-type converters or two second type of grid-type converters, the power of both parties is controlled through communication to reach an agreement. A grid-type converter may be connected to grid-type converters of the same type and different types at the same time, and it will be affected by both at the same time. The power control target P of each grid-type converter used to control the power output of the power supply is obtained in this way. tar As shown below:

[0047]

[0048] Where P tari is the power control target of the i-th grid-connected converter, α and β are the coefficients of the two communications, and the sum of α and β is 1, M i With N i k respectively represent the neighborhood set consisting of the same type of meshed converters that have communication connection with the i-th meshed converter and the neighborhood set consisting of different types of meshed converters that have communication connection with the i-th meshed converter; c is the coefficient of the type of the i-th grid-type converter. If the i-th grid-type converter is a first-type grid-type converter, then k c is 1, otherwise it is 0; T is the low-pass filter time constant, s is a complex variable, P i is the active power output of the power source connected to the i-th grid-connected converter, P jis the active power output of the power source connected to the jth grid-connected converter;

[0049] In this way, the P of each grid-connected converter is obtained. tar , and then apply it to the subsequent grid-connected converter control formula for power regulation.

[0050] In this way, in the communication between adjacent first-type meshed inverters and second-type meshed inverters, the high-frequency and low-frequency powers are reasonably distributed, and the communication between meshed inverters of the same type makes the powers of the two 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-type converters that combines VSG control and virtual impedance control. Each grid-type converter uses the hybrid energy storage control strategy for grid-type converters that combines VSG control and virtual impedance control to execute a power control target and obtain the voltage effective value and output frequency required to achieve hybrid energy storage.

[0052] The hybrid energy storage control strategy of the grid-type converter combining VSG control and virtual impedance control accurately and stably controls the power output of the grid-type converter by adding an additional frequency adjustment item to the traditional VSG control; at the same time, virtual impedance control is used to control the power change of the second type of grid-type converter when the load changes by applying a larger virtual inductance to the second type of grid-type converter than the first type of grid-type converter; through these two control methods (VSG control and virtual impedance control), the supercapacitor and the battery reasonably distribute power under the control of the grid-type converter, and the goal of the hybrid energy storage required by the supercapacitor to bear the high-frequency power and the battery to bear the low-frequency power is achieved;

[0053] The hybrid energy storage system needs to consider the respective energy storage characteristics, determine the respective power target values ​​in real time, and achieve reasonable and efficient distribution of power between battery energy storage and supercapacitor energy storage.

[0054] Unlike the hybrid energy storage in the DC microgrid system, the power distribution of the AC microgrid system cannot be achieved by adjusting the DC / DC circuit. In order to make the supercapacitors and batteries reach their respective power target values, it is necessary to discuss the control and power regulation methods of the grid-connected converter.

[0055] The VSG-controlled grid-type converter can provide inertial support for the AC microgrid system, is friendly to the operation of the AC microgrid system and is widely used. Therefore, this article discusses hybrid energy storage based on VSG control. The active-frequency control loop of the traditional VSG-controlled grid-type converter is as follows:

[0056]

[0057] 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 setting value controlled by VSG, P ref is the active power reference value of droop control, K ω is the active angular frequency droop coefficient, t is the time;

[0058] Normally, the active power-frequency control loop of the VSG will distribute the active power of each grid-type converter according to the droop characteristics, and obtain P = P m =P ref +K ω (ω n -ω). On the basis of VSG control, additional frequency adjustment items can be added to change the distribution result of active power to any reasonable distribution target;

[0059]

[0060] Among them, ω i is the angular frequency of the i-th grid-connected converter, ω vi is the frequency command value of the VSG control of the i-th grid-connected converter, e ωi is the frequency adjustment item of the i-th grid-connected converter, P mi is the active power setting value of the VSG control of the i-th grid-connected converter, P refi is the active power reference value of the droop control of the i-th grid-connected converter, K ω Frequency adjustment factor;

[0061] Through this approach, the purpose of allocating the low-frequency component of the total power to the battery as required by hybrid energy storage can be achieved. However, since the effect of frequency regulation on power output is relatively slow, the rapid power increase generated when the AC microgrid system is loaded cannot be well distributed by frequency regulation alone.

[0062] For the grid-type converter in the isolated AC microgrid system, since it always outputs three-phase AC power close to the rated voltage and rated frequency, when the load in the AC microgrid system changes, the second type of grid-type converter will also immediately bear the power, which is contrary to the goal of hybrid energy storage to only let the supercapacitor bear the high-frequency component. For the grid-type converter, the dynamic characteristics of active power will be affected by the output impedance of the power supply. The power supply with higher output impedance will bear less power changes when the load changes.

[0063] Therefore, virtual impedance control is applied to grid-connected converter control. By introducing a simulated impedance in the control calculation, the actual impedance can be simulated in terms of power supply characteristics. It is usually used to improve the stability of AC microgrid systems and optimize power distribution:

[0064]

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

[0066] When virtual impedance is used to compensate for the difference in actual impedance, the power response of different inverters can be made more consistent when facing load changes. If the output impedance of the battery is increased through virtual impedance, especially the virtual inductance which has a greater impact on power changes, the power distribution between the battery and the supercapacitor can be controlled so that the supercapacitor bears more power when the load changes. This change is consistent with the goal of making the supercapacitor bear the high-frequency component of power in hybrid energy storage.

[0067] L vB =L vC +L h

[0068] Among them, L vB is the virtual impedance of the grid-connected converter with the battery as the DC source, L vC is the virtual impedance of the grid-connected converter with supercapacitor as the DC source, L h It is the additional virtual impedance added to realize hybrid energy storage;

[0069] By applying the above power control method combining VSG control and virtual impedance control to a grid-type converter, it is possible to achieve power distribution of the supercapacitor and battery controlled by the grid-type converter according to the requirements of hybrid energy storage.

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

[0071] 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 distributed control method for a hybrid grid energy storage converter, characterized in that: The following steps are involved: S1. For an AC microgrid system including a supercapacitor, a battery, and a grid-type converter for controlling the supercapacitor and the battery, a sparse communication network is established for realizing 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 respectively, obtains its own active power through calculation, 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-connected converter implements the hybrid energy storage distributed control strategy according to the active power of neighboring nodes and its own type, and determines its own power control target. S4: Construct a hybrid energy storage control strategy for grid-type converters that combines VSG control and virtual impedance control. Each grid-type converter uses the hybrid energy storage control strategy for grid-type converters that combines VSG control and virtual impedance control to execute a power control target and obtain the voltage effective value and output frequency required to achieve hybrid energy storage. S5: The obtained voltage effective value and output frequency are transformed 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 distributed control method for hybrid grid energy storage converter according to claim 1, characterized in that: In the sparse communication network described in S1, each meshed converter is regarded as a node. If there is a communication connection between two nodes, they are called adjacent or neighbor nodes.

3. According to claim 1, a distributed control method for hybrid grid energy storage converter is characterized in that: The information in S1 includes active power.

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

5. A distributed control method for hybrid grid energy storage converter according to claim 4, characterized in that: The power control target in S3 is: Where P tari is the power control target of the i-th grid-connected converter, α and β are the coefficients of the two communications, and the sum of α and β is 1, M i With N i k respectively represent the neighborhood set consisting of the same type of meshed converters that have communication connection with the i-th meshed converter and the neighborhood set consisting of different types of meshed converters that have communication connection with the i-th meshed converter; c is the coefficient of the type of the i-th grid-type converter. If the i-th grid-type converter is a first-type grid-type converter, then k c is 1, otherwise it is 0; T is the low-pass filter time constant, s is a complex variable, P i is the active power output of the power source connected to the i-th grid-connected converter, P j is the active power output of the power supply connected to the jth grid-connected converter.

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

7. A distributed control method for hybrid grid energy storage converter according to claim 6, characterized in that: In the virtual impedance control, if the type of the grid-type converter is the first type of grid-type converter, the virtual inductance of the grid-type converter is L vC If the type of the grid-type converter is the second type grid-type converter, the virtual inductance of the grid-type converter is L vB : L vB =L vC +L h Among them, L vB is the virtual impedance of the grid-connected converter with the battery as the DC source, L vC is the virtual impedance of the grid-connected converter with supercapacitor as the DC source, L h It is the additional virtual impedance added to achieve hybrid energy storage.

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