Distributed coordination control method and system for multi-terminal MMC medium-voltage direct-current power distribution network

Abstract

The invention discloses a distributed coordination control method and system for a multi-terminal MMC medium-voltage direct-current power distribution network. The method comprises the following steps: acquiring an instruction and parameter information transmitted by an energy management center, wherein the parameter information at least comprises a power reference value; selecting a working mode according to the instruction; and calculating a corresponding control strategy according to the working mode and the output power information of the neighbor node converter in combination with a preset working mode algorithm. According to the distributed coordination control scheme, adjustable resources of all MMC converter stations can be fully called, for a system comprising N converter stations, the adjusting capacity of the distributed coordination control scheme is N times that of a traditional coordination scheme, and the flexibility of a power distribution network system and the capacity of absorbing new energy equipment are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current distribution networks, and in particular to a distributed coordinated control method and system for a multi-terminal MMC medium-voltage direct current distribution network. Background Art

[0002] In order to reduce the dependence on traditional fossil energy, distributed renewable energy generation is integrated in the distribution network in large quantities. Due to the intermittent and random shortcomings of renewable energy, higher requirements are placed on the absorption and regulation capabilities of the distribution network. At the same time, the high power quality requirements and strong load randomness of new loads such as charging piles and data centers have further challenges to the automatic regulation and stable operation capabilities of the distribution network.

[0003] Since new loads such as charging piles, data centers, and renewable energy generation often have DC characteristics, the integration of DC distribution networks has natural advantages. However, DC distribution networks based on traditional commutation technology have shortcomings such as limited regulation capabilities, severe harmonic interference, and poor flexibility. Multi-terminal medium-voltage DC distribution networks based on MMC converter technology can effectively overcome the limitations of traditional DC distribution networks and improve the system's ability to absorb renewable energy generation and new loads.

[0004] In order to achieve stable operation of the medium-voltage DC distribution system, multiple AC / DC converters in the system need to work in coordination to achieve voltage stability and power balance of the system. Traditional multi-terminal DC distribution systems often adopt a coordinated working mode of one master and multiple slaves. The master converter station is responsible for stabilizing voltage and power regulation, and the slave converter station is responsible for providing stable energy. This mode does not require communication between the converters, but there is a problem that the regulation capacity is restricted by the master converter station. The distributed coordinated working mode, by establishing a communication network between the converters, enables the converters to jointly take responsibility for stabilizing voltage and power regulation tasks, greatly improving the flexibility and regulation capacity of the system. Therefore, the effective integration of the master-slave coordinated working mode and the distributed coordinated working mode and their application in the multi-terminal MMC medium-voltage DC distribution network will further improve the stable working capacity of the system, maximize the adjustable capacity of the system, and adapt to the complex working conditions caused by various new energy sources and new loads. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above existing problems, the present invention is proposed.

[0007] Therefore, the present invention provides a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network, which can solve the problems mentioned in the background technology.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] In a first aspect, the present invention provides a multi-terminal MMC medium voltage DC distribution network distributed coordinated control system, comprising: at least three MMC converters, an MMC converter local control device corresponding to each MMC converter, a command receiving terminal, and an output control terminal;

[0010] The AC side of the MMC converter is connected to a 10KV AC grid, and the DC side is connected to a ±10KV DC distribution network;

[0011] The instruction receiving end is connected to the energy management center via Ethernet, and after receiving the instruction and parameter information from the energy management center, transmits the instruction to the MMC converter local control device, wherein the instruction is used to select the working mode of the MMC converter local control device, and the parameter information at least includes a power reference value;

[0012] The MMC converter local control device is used to perform valve control, current and voltage control, and coordinated control, and transmit the control strategy to the output control terminal;

[0013] Different MMC converters are connected by full-duplex communication, and the content of full-duplex communication transmission is the output power information of neighbor node converters.

[0014] As a preferred solution of the distributed coordinated control system of the multi-terminal MMC medium-voltage DC distribution network described in the present invention, wherein: the coordinated control includes master-slave coordinated control and distributed coordinated control;

[0015] The master-slave coordinated control includes selecting one MMC converter local control device as the master converter station, and the remaining MMC converter local control devices are all used as slave converter stations. The master converter station is used to undertake the voltage support and power regulation tasks of the DC distribution network, and the slave converter station is used to quantitatively provide rated power to the DC distribution network according to the power reference value provided by the energy management center;

[0016] The coordination process of the distributed coordinated control does not require intervention of the energy management center.

[0017] As a preferred solution of the distributed coordinated control system of the multi-terminal MMC medium-voltage DC distribution network described in the present invention, wherein: the MMC converter local control device includes: an MMC valve base control module, a current inner loop control module and a multi-terminal MMC converter coordinated control module;

[0018] The MMC valve base control module is used to control the MMC bridge arm submodule by adopting the nearest level modulation method according to the voltage reference signal, the input signal is the voltage reference signal output by the current inner loop control module, and the output signal is the switch control signal of the MMC bridge arm submodule;

[0019] The current inner loop control module is used to track the DC side current reference value, and its input signal is the current value collected on the DC side of the current reference signal output by the multi-terminal MMC converter coordination control module, and the output is a voltage reference signal;

[0020] The multi-terminal MMC converter coordination control module is used to coordinate the work between several MMC converters.

[0021] In a second aspect, the present invention provides a distributed coordinated control method for a multi-terminal MMC medium voltage DC distribution network, comprising:

[0022] Acquire instructions and parameter information transmitted by the energy management center, wherein the parameter information at least includes a power reference value;

[0023] Selecting a working mode according to the instruction, the working mode includes a master-slave coordinated control working mode and a distributed coordinated control working mode, and the master-slave coordinated control working mode and the distributed coordinated control working mode both include MMC valve base control and current inner loop control;

[0024] According to the working mode and the output power information of the neighbor node converter, combined with the preset working mode algorithm, the corresponding control strategy is calculated.

[0025] As a preferred solution of the distributed coordinated control method of the multi-terminal MMC medium-voltage DC distribution network of the present invention, wherein: the current inner loop control includes using the following algorithm to perform current inner loop control;

[0026]

[0027] Among them, I i (·) represents the DC side current of converter station i; Indicates the input current reference value; Indicates the voltage reference value output to the valve base control; represents the proportional and integral coefficients of the current inner loop controller, and t represents the time.

[0028] As a preferred solution of the distributed coordinated control method of the multi-terminal MMC medium-voltage DC distribution network described in the present invention, wherein: the master-slave coordinated control working mode includes the master converter station working in a constant voltage mode and the slave converter station working in a constant power mode;

[0029] The main converter station works in constant voltage mode and is used to undertake the voltage support and power regulation tasks of the DC distribution network. The voltage tracking algorithm it adopts is as follows:

[0030]

[0031] Among them, I k (·),V k (·) represents the DC side current and voltage of the converter in the main converter station; Represents the current reference value of the inner loop controller; V ref is the rated voltage of the DC distribution network; Represents the proportional and integral coefficients of the voltage tracking controller of the main converter station.

[0032] As a preferred solution of the distributed coordinated control method of the multi-terminal MMC medium-voltage DC distribution network of the present invention, the master-slave coordinated control working mode also includes:

[0033] The slave converter station works in constant power mode and is used to supply power to the DC distribution network according to the power reference value set by the energy management center. The power tracking algorithm used is as follows:

[0034]

[0035] in, I represents the current reference value of the inner loop controller from converter station i; i (·),V i (·) represent the power, current and voltage output from the DC side of converter i in the converter station, respectively; and Represents the proportional and integral coefficients of the power tracking controller of the slave converter station.

[0036] As a preferred solution of the distributed coordinated control method of the multi-terminal MMC medium-voltage DC distribution network described in the present invention, the distributed coordinated control working mode includes:

[0037] When working in the distributed coordinated control working mode, the MMC converter coordination controller at each end receives the output power information of the neighbor converter through the optical fiber communication connection, and sends the output power information of the MMC converter of the node collected by itself to the neighbor converter coordination controller. The multi-agent coordinated control algorithm is used to realize the equal distribution of the power required by the DC distribution network among the converters, and the tracking algorithm is used to realize the voltage support of the DC distribution network. The controller algorithm used for a single converter station i is as follows:

[0038]

[0039] in, represents the current reference value of the inner loop controller of converter station i; P i (·),P j (·) represents the output power of the converter at the i-th and j-th ends; a ij represents the weight of the optical fiber communication connection between the i-th and j-th converter controllers. If there is an optical fiber connection between the i-th and j-th converter controllers, then a ij >0, otherwise a ij =0; V represents the rated voltage of the DC side of the converter at the i-th end, which is set by the energy management center; i (·),I i (·) respectively represent the voltage and current on the DC side of the i-th converter; They represent the power and voltage correction on the DC side of the i-th converter respectively; and Respectively represent the proportional and integral coefficients of the power, voltage and droop regulation PI controllers; α i Is a normal number.

[0040] In a third aspect, the present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above-mentioned method when executing the computer program.

[0041] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the method described above when executed by a processor.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention proposes a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network, obtains instructions and parameter information transmitted by an energy management center, and the parameter information at least includes a power reference value; selects a working mode according to the instructions, and the working mode includes a master-slave coordinated control working mode and a distributed coordinated control working mode, and the master-slave coordinated control working mode and the distributed coordinated control working mode both include MMC valve base control and current inner loop control; according to the working mode and the output power information of the neighbor node converter, combined with the preset working mode algorithm, the corresponding control strategy is calculated. The present invention realizes the localized effective integration of coordinated control, inner loop control and valve base control, does not rely on a centralized controller or energy management center, and can achieve the voltage support and power balance goals of the DC distribution network only through data exchange between the local control devices of adjacent MMC converters. The present invention improves the robustness of the multi-terminal MMC medium-voltage distribution network; in the traditional coordinated control scheme, only one MMC converter station provides adjustable resources for the stable operation of the DC distribution network. The distributed coordinated control scheme proposed in the present invention can fully call upon the adjustable resources of all MMC converter stations. For a system including N converter stations, the adjustment capability of the distributed coordinated control scheme of the present invention is N times that of the traditional coordinated scheme, thereby improving the flexibility of the distribution network system and its ability to absorb new energy equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0044] Figure 1 A wiring diagram of a three-terminal MMC medium-voltage DC distribution network of a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network provided by an embodiment of the present invention;

[0045] Figure 2 A schematic diagram of a three-terminal MMC medium-voltage DC distribution network control system for a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network provided by an embodiment of the present invention;

[0046] Figure 3 A control system block diagram corresponding to an MMC converter station of a multi-terminal MMC medium-voltage DC distribution network distributed coordinated control method and system provided by an embodiment of the present invention;

[0047] Figure 4A schematic diagram of a three-terminal MMC converter station operating point change of a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network provided by an embodiment of the present invention;

[0048] Figure 5 A method flow chart of a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network provided by an embodiment of the present invention;

[0049] Figure 6 An internal structural diagram of a computer device of a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0050] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0051] Example 1

[0052] Reference Figure 1-Figure 6 , is the first embodiment of the present invention, which provides a multi-terminal MMC medium-voltage DC distribution network distributed coordinated control method and system, including a multi-terminal MMC medium-voltage DC distribution network distributed coordinated control method and a multi-terminal MMC medium-voltage DC distribution network distributed coordinated control system:

[0053] Before describing the embodiments of the present application in detail, some related concepts are first explained for the sake of clarity.

[0054] MMC bridge arm submodule: The MMC bridge arm submodule is the basic unit of MMC. MMC is usually composed of multiple bridge arms connected in series, and each bridge arm is composed of multiple submodules connected in series. The submodule generally contains two switching devices (such as IGBT) and a capacitor, which can store energy and release it at the right time to help form the required DC or AC voltage. The switching state of the submodule is determined by the control signal to generate the required voltage waveform.

[0055] MMC valve base control: MMC valve base control refers to the process of controlling the bridge arm submodule in the MMC. It involves adjusting the switching state of the submodule according to system requirements to achieve precise control of the output voltage. This is usually achieved through techniques such as Nearest Level Modulation (NLM) to make the output voltage of the MMC as close as possible to the required reference voltage waveform while minimizing switching losses and improving efficiency.

[0056] Current inner loop control: Current inner loop control is a closed-loop control strategy used to ensure that the DC side current (or other control variables) of the MMC can quickly and accurately track a given reference value. This control is usually implemented using a proportional-integral (PI) controller, which can adjust the voltage reference signal in real time to compensate for any deviations, thereby keeping the current stable.

[0057] Coordinated control: In a multi-terminal MMC system, coordinated control is a control method that must be performed between each MMC converter in order to achieve stable operation and power balance of the entire system. The goal of coordinated control is to ensure that all converters work together to maintain the stability of the DC bus voltage, and to reasonably distribute power to avoid overload or underload.

[0058] Coordinated control of multi-terminal MMC converters: Coordinated control of multi-terminal MMC converters refers to the system with multiple MMC converters, which enables all converters to share information such as power, voltage and current data through a communication network, so as to achieve global optimal power allocation and system stability. This control mechanism may involve complex algorithms, such as multi-agent systems (MAS) algorithms, to handle the interaction and decision-making between multiple terminals.

[0059] Master-slave coordination: Master-slave coordination is a centralized control strategy in which one converter is designated as the master converter responsible for controlling the DC voltage and power balance, while the other converters, as slave converters, follow the instructions of the master converter and perform specific tasks, such as providing fixed power or responding to changes in power demand. The master converter usually needs to receive instructions from the energy management center, and the slave converters adjust their operations according to these instructions.

[0060] Distributed coordination: Distributed coordination is a decentralized control strategy in which there is no single control center. Each converter has a certain degree of autonomy and can make decisions based on local information (such as data from neighboring converters). Through full-duplex communication, converters can exchange power information in real time and jointly achieve stable operation and power balance of the system without direct intervention from the central dispatcher.

[0061] In the existing technology, multi-terminal MMC medium-voltage DC distribution networks usually face complex control challenges, especially when new energy devices are widely connected. With the rapid development of renewable energy, such as wind power and solar energy, the energy structure in the power grid is undergoing profound changes. These new energy devices are intermittent and volatile, which brings new challenges to the stable operation of the power grid.

[0062] The present application provides a method that can effectively solve the above-mentioned problems. Next, multiple embodiments will be combined to explain in detail how to implement the multi-terminal MMC medium-voltage DC distribution network distributed coordinated control system;

[0063] like Figure 1 As shown, it is a wiring diagram of a three-terminal MMC medium-voltage DC distribution network of a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network applicable to the present invention, which includes three MMC converter stations. The AC side of each MMC converter station is connected to an external AC power supply line through a transformer, and the DC side is connected to a ±10kV DC bus, and is further connected to a DC distribution network to achieve effective integration of DC loads such as photovoltaics, energy storage, and charging piles. The scope of application of the present invention is not limited to this embodiment, and any number of multi-terminal MMC DC distribution systems are applicable to the present invention.

[0064] Figure 2 A schematic diagram of a three-terminal MMC medium-voltage DC distribution network control system of a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network is shown. The integrated energy management system in the figure is connected to the local control device of each MMC converter station via an Ethernet connected to a data server, so as to realize real-time monitoring of the working state and working mode control of the MMC converter station (the converter station in the figure is the local control device). Figure 2 The controllers of MMC1, MMC2 and MMC2, MMC3 are connected through full-duplex optical fiber communication to achieve real-time data interaction. For any multi-terminal MMC system, the coordinated control method of the present invention requires the topology of the optical fiber communication network to have connectivity, that is, there is a communication path from any node in the optical fiber network to any other node. Apart from this, there are no other special requirements. Each MMC controller integrates coordinated control, inner loop control and valve base control functions, collects voltage and current signals of the MMC converter station in real time, and finally outputs valve control instructions to the MMC converter through calculations of each control unit to achieve system control goals.

[0065] The specific multi-terminal MMC medium voltage DC distribution network distributed coordinated control system includes: at least three MMC converters, an MMC converter local control device corresponding to each MMC converter, a command receiving terminal and an output control terminal;

[0066] The AC side of the MMC converter is connected to the 10KV AC grid, and the DC side is connected to the ±10KV DC distribution network;

[0067] The instruction receiving end is connected to the energy management center via Ethernet, and after receiving the instruction and parameter information from the energy management center, transmits the instruction to the MMC converter local control device, where the instruction is used to select the working mode of the MMC converter local control device, and the parameter information at least includes a power reference value;

[0068] The local control device of the MMC converter is used to perform valve control, current and voltage control, and coordinated control, and transmit the control strategy to the output control terminal;

[0069] It should be noted that different MMC converters are connected by full-duplex communication, and the content of full-duplex communication transmission is the output power information of the neighbor node converter.

[0070] In the embodiment of the present application, the coordinated control includes master-slave coordinated control and distributed coordinated control;

[0071] The master-slave coordinated control includes selecting one MMC converter local control device as the master converter station, and the other MMC converter local control devices are all slave converter stations. The master converter station is used to undertake the voltage support and power regulation tasks of the DC distribution network, and the slave converter station is used to quantitatively provide rated power to the DC distribution network according to the power reference value provided by the energy management center;

[0072] The coordination process of distributed coordinated control does not require the intervention of the energy management center.

[0073] It should be noted that when new energy equipment is intermittent and volatile, distributed coordinated control strategies can ensure the stable operation of the system and optimize power distribution to avoid overload or underload.

[0074] In the embodiments of the present application, Figure 3 As shown, it is a system block diagram of the MMC converter local control device, and the MMC converter local control device includes: an MMC valve base control module, a current inner loop control module and a multi-terminal MMC converter coordination control module;

[0075] The MMC valve base control module is used to control the MMC bridge arm submodule by adopting the nearest level modulation method according to the voltage reference signal. The input signal is the voltage reference signal output by the current inner loop control module, and the output signal is the switch control signal of the MMC bridge arm submodule.

[0076] The current inner loop control module is used to track the DC side current reference value. Its input signal is the current value collected on the DC side of the current reference signal output by the multi-terminal MMC converter coordination control module, and its output is a voltage reference signal.

[0077] The multi-terminal MMC converter coordination control module is used to coordinate the work between several MMC converters.

[0078] In an optional embodiment, the multi-terminal MMC converter coordination control module can also integrate energy management functions, and can dynamically adjust the power distribution of each MMC converter according to the real-time operation of the DC distribution network and the output of the new energy equipment to achieve the optimal energy configuration. This function collects the operating status information of each MMC converter, the voltage and current information of the DC distribution network, and the output information of the new energy equipment in real time, and combines the preset energy management strategy to calculate the optimal power reference value of each MMC converter, and transmits these reference values ​​to the corresponding MMC converter local control device through the instruction receiving end.

[0079] Exemplarily, the system collects the following information in real time: operating status information of each MMC converter, including but not limited to the DC side voltage, DC side current and active power P of the converter; i The voltage and current information of the DC distribution network, including the DC bus voltage V bus and the total current I total Output information of new energy equipment, including real-time power output of solar photovoltaic panels, wind turbines, etc. j RE , where j represents different renewable energy devices.

[0080] Furthermore, according to a pre-set energy management strategy, such as maximizing the utilization rate of renewable energy, minimizing system losses or maintaining voltage stability, the optimal power reference value of each MMC converter is calculated. This may involve solving an optimization problem. The objective function and constraints in the exemplary embodiment selected in this application are as follows:

[0081] Assuming the goal is to minimize system losses, the objective function is defined as the weighted sum of all converter losses:

[0082]

[0083] Among them, L i is the loss of the ith converter, w i is the weight factor, N is the total number of converters;

[0084] Constraints:

[0085] st

[0086]

[0087] V min ≤V bus ≤V max

[0088] Among them, P load is the total power demand of the system load, P loss is the system loss, V bus Indicates the DC bus voltage;

[0089] Use appropriate optimization algorithms (such as gradient descent method, genetic algorithm or linear programming) to solve the above optimization problem and obtain the optimal power reference value of each MMC converter

[0090] The calculated optimal power reference value The command is transmitted to the corresponding MMC converter local control device through the command receiving end to update the control strategy.

[0091] In addition, in order to further improve the stability and reliability of the system, the multi-terminal MMC converter coordination control module also has fault detection and fault tolerance capabilities. Once a fault or abnormality is detected in a certain MMC converter, the coordination control module will immediately start the fault tolerance mechanism, adjust the power distribution of other MMC converters, ensure the stable operation of the DC distribution network, and transmit the fault information to the energy management center via Ethernet for timely fault handling and maintenance.

[0092] In the distributed coordinated control strategy, each MMC converter exchanges power information in real time through full-duplex communication to jointly achieve stable operation and power balance of the system. This decentralized control strategy not only improves the flexibility and scalability of the system, but also reduces the dependence on central scheduling and enhances the system's anti-interference ability.

[0093] The multi-terminal MMC medium-voltage DC distribution network distributed coordination control system provided by this application can not only effectively solve the challenges brought by the widespread access of new energy equipment, but also optimize the power distribution of the system and improve the stability and reliability of the system. At the same time, the system also has fault detection and fault tolerance capabilities, which can ensure that the DC distribution network can still operate stably in the event of a fault or abnormal situation, providing a strong guarantee for the safe and efficient operation of the power system.

[0094] This embodiment also provides a distributed coordinated control method for a multi-terminal MMC medium-voltage DC distribution network, including:

[0095] Obtaining instructions and parameter information transmitted by the energy management center, where the parameter information at least includes a power reference value;

[0096] Select the working mode according to the instruction. The working modes include master-slave coordinated control working mode and distributed coordinated control working mode. Both the master-slave coordinated control working mode and the distributed coordinated control working mode include MMC valve base control and current inner loop control;

[0097] According to the working mode and the output power information of the neighbor node converter, combined with the preset working mode algorithm, the corresponding control strategy is calculated.

[0098] In the embodiment of the present application, the current inner loop control includes using the following algorithm to perform the current inner loop control;

[0099]

[0100] Among them, I i (·) represents the DC side current of converter station i; Indicates the input current reference value; Indicates the voltage reference value output to the valve base control; represents the proportional and integral coefficients of the current inner loop controller, and t represents the time.

[0101] In the embodiment of the present application, the master-slave coordinated control working mode includes the master converter station working in a constant voltage mode and the slave converter station working in a constant power mode;

[0102] In the embodiment of the present application, the main converter station operates in a constant voltage mode to undertake the voltage support and power regulation tasks of the DC distribution network. The voltage tracking algorithm adopted is as follows:

[0103]

[0104] Among them, I k (·),V k (·) represents the DC side current and voltage of the converter in the main converter station; Represents the current reference value of the inner loop controller; V ref is the rated voltage of the DC distribution network; Represents the proportional and integral coefficients of the voltage tracking controller of the main converter station.

[0105] In the embodiment of the present application, the master-slave coordinated control working mode also includes:

[0106] The slave converter station works in constant power mode and is used to supply power to the DC distribution network according to the power reference value set by the energy management center. The power tracking algorithm used is as follows:

[0107]

[0108] in, I represents the current reference value of the inner loop controller from converter station i; i (·),V i (·) represent the power, current and voltage output from the DC side of converter i in the converter station, respectively; and Represents the proportional and integral coefficients of the power tracking controller of the slave converter station.

[0109] In the embodiment of the present application, the distributed coordinated control working mode includes:

[0110] When working in the distributed coordinated control working mode, the MMC converter coordination controller at each end receives the output power information of the neighbor converter through the optical fiber communication connection, and sends the output power information of the MMC converter of the node collected by itself to the neighbor converter coordination controller. The multi-agent coordinated control algorithm is used to realize the equal distribution of the power required by the DC distribution network among the converters, and the tracking algorithm is used to realize the voltage support of the DC distribution network. The controller algorithm used for a single converter station i is as follows:

[0111]

[0112] in, represents the current reference value of the inner loop controller of converter station i; P i (·),P j (·) represents the output power of the converter at the i-th and j-th ends; a ij represents the weight of the optical fiber communication connection between the i-th and j-th converter controllers. If there is an optical fiber connection between the i-th and j-th converter controllers, then a ij >0, otherwise a ij =0; V represents the rated voltage of the DC side of the converter at the i-th end, which is set by the energy management center; i (·),I i (·) respectively represent the voltage and current on the DC side of the i-th converter; They represent the power and voltage correction on the DC side of the i-th converter respectively; and Respectively represent the proportional and integral coefficients of the power, voltage and droop regulation PI controllers; α i Is a normal number.

[0113] In an optional embodiment, the above control strategy can be further optimized according to the operation status of the DC distribution network and the system stability requirements. Specifically, the controller's proportional and integral coefficients can be dynamically adjusted by real-time monitoring of key parameters such as voltage, current and power of the DC distribution network to adapt to optimal control under different working conditions. The optional implementation steps are as follows:

[0114] Real-time monitoring of key parameters of the DC distribution network, such as DC side voltage, current, power, frequency, and output power of each converter, filtering and smoothing the collected data to eliminate noise and ensure data quality;

[0115] Based on real-time monitoring data, evaluate the current status of the system, including but not limited to: whether the system is in a high load or low load state, whether there are voltage or frequency fluctuations, and whether the output of renewable energy has changed significantly;

[0116] Based on the results of the system status assessment, determine whether the PI controller parameters need to be adjusted. Usually, when the load is high or the system is unstable, increase the proportional coefficient K. p To speed up the response; when the load is low or the system is relatively stable, increase the integral coefficient K i To improve steady-state accuracy.

[0117] Dynamically adjust PI controller parameters based on preset rules or algorithms. For example, fuzzy logic, neural networks, or adaptive algorithms can be used to adjust K p and K i For example, if the current system detects a large voltage fluctuation, in order to quickly suppress the voltage fluctuation, the proportional coefficient K can be temporarily increased. p If it is detected that the system is in a steady state for a long time but has a slight deviation, the integral coefficient K can be appropriately increased. i To improve steady-state performance.

[0118] The adjusted parameters are applied to the PI controller of each MMC converter to implement the new control strategy.

[0119] For example, assume a three-terminal MMC medium voltage DC distribution network system with a system voltage target of 10 kV. The currently monitored voltage fluctuation range is between 9.8 kV and 10.2 kV. The system is in a high load state and there is obvious voltage fluctuation.

[0120] The initial parameters are set as: initial proportional coefficient K p =10; initial integration coefficient K i =0.1;

[0121] Real-time monitoring data: system average voltage V avg =10.0kV; voltage fluctuation range ΔV = 0.4kV, system power P sys =10MW;

[0122] Since the system is under high load and there are voltage fluctuations, a quick response is required to stabilize the voltage and the proportional coefficient K is temporarily increased. p to 15 to improve the system's response speed to voltage fluctuations. After adjustment, the system can suppress voltage fluctuations more quickly, the average voltage is stabilized around 10.0kV, and the voltage fluctuation range is reduced to within 0.2kV. After the system returns to stability, the parameters can be adjusted again to a value more suitable for steady-state operation.

[0123] In an optional embodiment, possible uncertainties and disturbances in the DC distribution network may also be taken into account, such as the volatility of renewable energy and changes in load, and more advanced control methods such as predictive control, adaptive control or robust control may be used to improve the stability and reliability of the system.

[0124] Predictive control can predict the system state in the future based on historical data and prediction models, and adjust the control strategy accordingly to achieve optimal control of the future system state. Adaptive control can automatically adjust the control parameters according to the actual operation of the system to adapt to the changes and uncertainties of the system parameters. Robust control can maintain the stability of system performance and reduce the impact of disturbances on the system when the system is subject to external disturbances.

[0125] In an optional embodiment, in order to improve the energy efficiency and environmental performance of the DC distribution network, energy management and optimization strategies can also be introduced to intelligently dispatch and optimize the energy in the system. For example, the working mode and power distribution of the converter station can be dynamically adjusted according to the power generation of renewable energy and load demand to achieve full and efficient use of energy.

[0126] In summary, the present invention proposes a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network, obtains instructions and parameter information transmitted by an energy management center, and the parameter information at least includes a power reference value; selects a working mode according to the instructions, and the working mode includes a master-slave coordinated control working mode and a distributed coordinated control working mode, and the master-slave coordinated control working mode and the distributed coordinated control working mode both include MMC valve base control and current inner loop control; according to the working mode and the output power information of the neighbor node converter, combined with a preset working mode algorithm, the corresponding control strategy is calculated. The present invention realizes the localized effective integration of coordinated control, inner loop control and valve base control, does not rely on a centralized controller or energy management center, and can achieve the voltage support and power balance goals of the DC distribution network only through data exchange between local control devices of adjacent MMC converters. The present invention improves the robustness of the multi-terminal MMC medium-voltage distribution network; in the traditional coordinated control scheme, only one MMC converter station provides adjustable resources for the stable operation of the DC distribution network. The distributed coordinated control scheme proposed in the present invention can fully call upon the adjustable resources of all MMC converter stations. For a system including N converter stations, the adjustment capability of the distributed coordinated control scheme of the present invention is N times that of the traditional coordination scheme, thereby improving the flexibility of the distribution network system and its ability to absorb new energy equipment.

[0127] The above-mentioned unit modules may be embedded in or independent of the processor in the computer device in the form of hardware, or may be stored in the memory in the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above-mentioned modules.

[0128] This embodiment also provides a computer device, which may be a terminal, and its internal structure diagram may be as shown in FIG. Figure 6 As shown. The computer device includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, an operator network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, a distributed coordinated control method for a multi-terminal MMC medium-voltage DC distribution network is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covered on the display screen, or a button, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse.

[0129] This embodiment further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the following steps are implemented:

[0130] Obtaining instructions and parameter information transmitted by the energy management center, where the parameter information at least includes a power reference value;

[0131] Select the working mode according to the instruction. The working modes include master-slave coordinated control working mode and distributed coordinated control working mode. Both the master-slave coordinated control working mode and the distributed coordinated control working mode include MMC valve base control and current inner loop control;

[0132] According to the working mode and the output power information of the neighbor node converter, combined with the preset working mode algorithm, the corresponding control strategy is calculated.

[0133] Example 2

[0134] Reference Figure 2-Figure 5 , which is an embodiment of the present invention, provides a distributed coordinated control method and system for a multi-terminal MMC medium-voltage DC distribution network. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through experiments.

[0135] like Figure 4As shown, the changes of the working point of the MMC converter station in the master-slave coordination mode;

[0136] Figure 4 In (a), the system works at working point 1, MMC3 is set as the master converter station, working in a constant DC voltage state, and MMC1 and MMC2 are set as slave converter stations, working in a constant DC power state;

[0137] Figure 4 In (b), MMC3 is out of operation for some reason, the voltage of MMC1 and MMC2 drops and reaches the second working point. MMC2 becomes the new master converter station and works in the constant voltage mode. MMC1 is still the slave converter station and works at another constant power point.

[0138] Figure 4 In (c), MMC3 and MMC2 both exit operation for some reason, the voltage of MMC1 drops and reaches the working point three. MMC1 becomes the new main converter station and operates in the constant voltage mode.

[0139] When each MMC converter station operates in distributed coordination mode, after any MMC stops working, the remaining MMC converter stations continue to coordinate and undertake voltage stability and power balance tasks without the need for mode switching.

[0140] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0141] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of complete hardware embodiments, complete software embodiments, or embodiments in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiments of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0142] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0143] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0144] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0145] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0146] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A multi-terminal MMC medium voltage DC distribution network distributed coordinated control system, characterized in that: include: At least three MMC converters, an MMC converter local control device corresponding to each MMC converter, a command receiving terminal and an output control terminal; The AC side of the MMC converter is connected to a 10KV AC grid, and the DC side is connected to a ±10KV DC distribution network; The instruction receiving end is connected to the energy management center via Ethernet, and after receiving the instruction and parameter information from the energy management center, transmits the instruction to the MMC converter local control device, wherein the instruction is used to select the working mode of the MMC converter local control device, and the parameter information at least includes a power reference value; The MMC converter local control device is used to perform valve control, current and voltage control, and coordinated control, and transmit the control strategy to the output control terminal; Different MMC converters are connected by full-duplex communication, and the content of full-duplex communication transmission is the output power information of neighbor node converters.

2. The multi-terminal MMC medium voltage DC distribution network distributed coordinated control system according to claim 1, characterized in that: The coordinated control includes master-slave coordinated control and distributed coordinated control; The master-slave coordinated control includes selecting one MMC converter local control device as the master converter station, and the remaining MMC converter local control devices are all used as slave converter stations. The master converter station is used to undertake the voltage support and power regulation tasks of the DC distribution network, and the slave converter station is used to quantitatively provide rated power to the DC distribution network according to the power reference value provided by the energy management center; The coordination process of the distributed coordinated control does not require intervention of the energy management center.

3. The multi-terminal MMC medium voltage DC distribution network distributed coordinated control system according to claim 2, characterized in that: The MMC converter local control device comprises: an MMC valve base control module, a current inner loop control module and a multi-terminal MMC converter coordination control module; The MMC valve base control module is used to control the MMC bridge arm submodule by adopting the nearest level modulation method according to the voltage reference signal, the input signal is the voltage reference signal output by the current inner loop control module, and the output signal is the switch control signal of the MMC bridge arm submodule; The current inner loop control module is used to track the DC side current reference value, and its input signal is the current value collected on the DC side of the current reference signal output by the multi-terminal MMC converter coordination control module, and the output is a voltage reference signal; The multi-terminal MMC converter coordination control module is used to coordinate the work between several MMC converters.

4. A control method applied to the distributed coordinated control system of the multi-terminal MMC medium voltage DC distribution network according to claim 1, characterized in that: The control method comprises: Acquire instructions and parameter information transmitted by the energy management center, wherein the parameter information at least includes a power reference value; Selecting a working mode according to the instruction, the working mode includes a master-slave coordinated control working mode and a distributed coordinated control working mode, and the master-slave coordinated control working mode and the distributed coordinated control working mode both include MMC valve base control and current inner loop control; According to the working mode and the output power information of the neighbor node converter, combined with the preset working mode algorithm, the corresponding control strategy is calculated.

5. The distributed coordinated control method for a multi-terminal MMC medium voltage DC distribution network according to claim 4, characterized in that: The current inner loop control includes using the following algorithm to perform current inner loop control; Among them, I i (·) represents the DC side current of converter station i; Indicates the input current reference value; Indicates the voltage reference value output to the valve base control; represents the proportional and integral coefficients of the current inner loop controller, and t represents the time.

6. The distributed coordinated control method for a multi-terminal MMC medium voltage DC distribution network according to claim 5, characterized in that: The master-slave coordinated control working mode includes the master converter station working in a constant voltage mode and the slave converter station working in a constant power mode; The main converter station works in constant voltage mode and is used to undertake the voltage support and power regulation tasks of the DC distribution network. The voltage tracking algorithm it adopts is as follows: Among them, I k (·),V k (·) represents the DC side current and voltage of the converter in the main converter station; Represents the current reference value of the inner loop controller; V ref is the rated voltage of the DC distribution network; Represents the proportional and integral coefficients of the voltage tracking controller of the main converter station.

7. The distributed coordinated control method for a multi-terminal MMC medium voltage DC distribution network according to claim 6, characterized in that: The master-slave coordinated control working mode also includes: The slave converter station works in constant power mode and is used to supply power to the DC distribution network according to the power reference value set by the energy management center. The power tracking algorithm used is as follows: in, I represents the current reference value of the inner loop controller from converter station i; i (·),V i (·) represent the power, current and voltage output from the DC side of converter i in the converter station, respectively; and Represents the proportional and integral coefficients of the power tracking controller of the slave converter station.

8. The distributed coordinated control method for a multi-terminal MMC medium voltage DC distribution network according to claim 7, characterized in that: The distributed coordinated control working mode includes: When working in the distributed coordinated control working mode, the MMC converter coordination controller at each end receives the output power information of the neighbor converter through the optical fiber communication connection, and sends the output power information of the MMC converter of the node collected by itself to the neighbor converter coordination controller. The multi-agent coordinated control algorithm is used to realize the equal distribution of the power required by the DC distribution network among the converters, and the tracking algorithm is used to realize the voltage support of the DC distribution network. The controller algorithm used for a single converter station i is as follows: in, represents the current reference value of the inner loop controller of converter station i; P i (·),P j (·) represents the output power of the converter at the i-th and j-th ends; a ij represents the weight of the optical fiber communication connection between the i-th and j-th converter controllers. If there is an optical fiber connection between the i-th and j-th converter controllers, then a ij >0, otherwise a ij =0; V represents the rated voltage of the DC side of the converter at the i-th end, which is set by the energy management center; i (·),I i (·) respectively represent the voltage and current on the DC side of the i-th converter; They represent the power and voltage correction on the DC side of the i-th converter respectively; and Respectively represent the proportional and integral coefficients of the power, voltage and droop regulation PI controllers; α i Is a normal number.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 4 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 4 to 8 are implemented.

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