Control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging, device and medium

Abstract

The present invention relates to a control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging, a device, and a medium, wherein the method implements a hierarchical management of the energy storage converters based on the state of charge (SOC) values ​​of the energy storage devices. The high-priority converter is switched to variable-speed (VSG) mode, and it is determined whether the voltage and frequency fluctuations of the microgrid exceed the deadband for control. If frequency fluctuations exceed the deadband, the active power output is adjusted via VSG mode; if voltage fluctuations exceed the deadband, the reactive power output is adjusted. The energy storage devices are switched to VSG mode stepwise.If demand cannot be met, photovoltaic systems and electric vehicles are connected sequentially to support the grid. Before connecting a photovoltaic system, its voltage is synchronized with the voltage of the already connected energy storage devices, and the photovoltaic system is switched to grid stabilization (VSG) mode. Should further support be required, the charging station control algorithm must be adapted to allow the feed-in of power from electric vehicles. Before connecting an electric vehicle, voltage and phase must also be synchronized to enable coordinated support of the microgrid. This procedure significantly improves the voltage and frequency stability of the microgrid system.

Description

TECHNICAL AREA

[0001] The present invention relates to the field of microgrid control, in particular a control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging, a device and a medium. STATE OF THE ART

[0002] A hybrid AC / DC microgrid with photovoltaics, energy storage, and charging consists of a photovoltaic unit, an energy storage unit, a charging station, etc. Fully leveraging the benefits of clean photovoltaic energy, along with the peak load reduction and off-peak load supplementation capabilities of energy storage, enables the construction of a green, low-carbon park with integrated power generation, grid, load, and energy storage infrastructure coupled to the park's electricity demand. This reduces carbon emissions and increases economic viability. The intermittent and fluctuating nature of photovoltaic power generation can easily lead to instabilities in the microgrid's frequency and voltage.Current microgrid systems primarily employ line-following (GFL) converters, which are grid-coupled, cannot actively respond to changes in grid frequency and voltage, and lack both inertia and attenuation capabilities. Consequently, they cannot provide frequency and voltage support and regulation. In contrast, line-forming (GFM) converters can offer inertial support to the microgrid and possess some active support capability. However, research into existing inventions regarding voltage and frequency support methods in microgrids is not sufficiently comprehensive.Therefore, the question of how to propose a comprehensive procedure for establishing and maintaining the bus voltage and actively supporting the voltage and frequency of the microgrid in the event of voltage and frequency fluctuations in the hybrid AC / DC microgrid system with photovoltaics, energy storage and charging has become a critical problem that urgently needs to be solved.

[0003] Regarding grid-forming control methods for new energy substations, Chinese patent no. CN118232365A discloses a control method for new energy substations based on grid-forming technology and a corresponding device. This invention proposes a control method for supporting the grid frequency using station-based energy storage, photovoltaics, and wind power at a grid-connected new energy substation. In this method, the station-based energy storage devices are classified according to their droop coefficients. When grid frequency fluctuations exceed the deadband for control, the energy storage devices stepwise support the grid voltage and frequency. Subsequently, the capacity deficit after energy storage support is calculated to determine the required feed-in of photovoltaics and wind power.This invention primarily concerns grid-connected microgrids for new energy stations. Its topology does not account for hybrid AC / DC microgrids. When multiple energy storage units are operated in parallel, the problem of state-of-charge (SOC) balancing between the energy storage units cannot be adequately addressed, nor can the amplitude and phase synchronization problems during the parallel operation of converters in VSG (Virtual Synchronous Generator) mode. CONTENT OF THE PRESENT INVENTION

[0004] The present invention relates to a control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging, a device and a medium. Its aim is to solve the problem of how to dynamically adjust the number of energy storage devices, photovoltaic systems and electric vehicles in a microgrid during the transition from grid-connected to island operation in order to stabilize the voltage and frequency of the microgrid, improve the autonomous control capability of the system and reduce costs.

[0005] To achieve the aforementioned objectives, the present invention provides, in a first aspect, a control method for constructing a hybrid AC / DC microgrid with photovoltaics, energy storage, and charging, comprising the following steps: classifying the energy storage converters from high to low based on the SOC values ​​of the energy storage devices; switching the operating mode of the energy storage converter with the highest priority from PQ mode to VSG mode; detecting the voltage and frequency of the microgrid and determining whether the fluctuation range of the voltage and frequency of the microgrid exceeds the deadband range for control;

[0006] Calculate, if the frequency fluctuation in the microgrid exceeds the deadband range for the control, the required active power compensation via the active power frequency control in VSG mode, and adjust the active power output of the microgrid and the energy storage devices;

[0007] Adjust, if the voltage fluctuation in the microgrid exceeds the deadband range for control, the reactive power output of the microgrid and the energy storage devices via the reactive power voltage control in VSG mode;

[0008] Acquiring the SOC values ​​of the energy storage devices, adjusting the operating modes of the energy storage devices stepwise in descending order of the SOC values ​​and switching from PQ mode to VSG mode, synchronizing, using a synchronization control module, the voltage amplitude and phase angle of this energy storage converter with those of the energy storage converters already operating in VSG mode, and stepwise supporting the voltage and frequency of the microgrid by the energy storage devices;

[0009] Connecting the photovoltaic devices to the AC bus in descending order of adjustable capacities if all energy storage devices cannot respond to voltage and frequency fluctuations in the microgrid after switching to VSG mode; synchronizing, before connecting the photovoltaic device, the voltage amplitude and phase angle of the DC / AC converter of the photovoltaic device with those of the already connected energy storage devices using the synchronization control module;

[0010] Switching the operating mode of the photovoltaic device from PQ mode to VSG mode in order to support the voltage and frequency of the microgrid together with the energy storage unit;

[0011] Adapting the control algorithm for the charging station and building up the voltage of the microgrid by feeding power from electric vehicles into the microgrid, if it is still not possible to fully react to the voltage and frequency fluctuations of the microgrid;

[0012] Synchronize, prior to connecting the electric vehicle, the voltage amplitude and phase of the electric vehicle's charging station with the voltage amplitude and phase angle of the already connected energy storage converters using the synchronization control module; control, using the synchronization control module, the electric vehicle's battery to support the voltage and frequency of the microgrid together with the energy storage devices and the photovoltaic array.

[0013] Furthermore, the procedure for classifying energy storage converters based on the SOC values ​​of the energy storage devices from high to low includes the following: Recording the SOC values ​​of the respective energy storage devices; Sorting the SOC values ​​of the energy storage devices and setting the priorities of the respective energy storage devices to respond to fluctuations in the microgrid based on the SOC values ​​in descending order; Distributing the power required for regulation to the respective energy storage devices in sequential order and allocating the power based on priority and maximum charging / discharging power until the power allocation is complete.

[0014] Furthermore, the procedure for distributing the power required for the control to the respective energy storage devices in sequential order and allocating the power according to priority and maximum charging / discharging power, until the power allocation is completed, includes the following: Initializing the power to be allocated, which is required to respond to frequency and voltage fluctuations in the microgrid;

[0015] Iterate through the respective energy storage devices and select the PCS of the energy storage device with the highest priority as the current PCS, whereby, if the maximum charge / discharge power of the current PCS is less than the power to be allocated, set the maximum charge / discharge power of the current PCS as the charge / discharge power of the current PCS and subtract the charge / discharge power of the current PCS from the power to be allocated to obtain the new power to be allocated; otherwise, set the power to be allocated as the charge / discharge power of the current PCS;

[0016] Determine if all PCS have been completed, if the cycle is incomplete, proceed to the previous step, otherwise determine that the control capability of the energy storage unit has reached its saturation limit, exit and close.

[0017] Furthermore, the active power frequency control in VSG mode calculates the required active power compensation based on the rotor characteristics of synchronous generators using the rotor motion equation, with the exact calculation formula being as follows: P=Jω0dωdt+Dω0(ω−ω0)

[0018] Here, P denotes the active power compensation required for the system to reach the target frequency, J denotes the coefficient of inertia of the virtual synchronous generator, ω0 denotes the nominal angular frequency, and ω denotes the output angular frequency of the VSG. dωdt denotes the rate of change of the angular frequency and D denotes the damping coefficient of the virtual synchronous generator.

[0019] Furthermore, the formula for calculating the change in active power due to the inertial reaction in VSG mode is: PInertia=−TJfN×dfdt×PN

[0020] Here, P denotes Inertia the change in the active power of the microgrid during the inertial response, T J denotes the equivalent time constant of inertia, f N denotes the nominal frequency of the microgrid system dfdt denotes the frequency change rate of the micronetwork and P N denotes the nominal active power of the network-forming device.

[0021] The formula for calculating the damping power in VSG mode is: PDamping=D(ω−ω0)

[0022] Here, P denotes DampingThe damping active power provided by the virtual synchronous generator, D denotes the damping coefficient of the virtual synchronous generator, ω0 denotes the nominal angular frequency and ω denotes the output angular frequency of the VSG.

[0023] Furthermore, the formula for calculating reactive power voltage control in VSG mode is: ΔU=Dq(Qref−Qe)+(Uref−U)

[0024] Here, ΔU denotes the change in voltage, D q denotes the reactive power droop coefficient, Q ref denotes the reactive power setpoint, Q e denotes the reactive power output of the converter, U ref denotes the voltage setpoint and U denotes the output voltage amplitude of the converter.

[0025] Furthermore, the control steps of the synchronization control module are as follows: Control, using the synchronization control module, the voltage amplitude and phase of the energy storage device, the photovoltaic device or the electric vehicle charging station converter, so that it corresponds to the voltage amplitude and phase of the already connected VSG converters, thereby ensuring that the instantaneous voltage values ​​have a difference of zero when the respective converters are operated in parallel in VSG mode;

[0026] Adjusting the phase control step size and amplitude control step size based on the differences in voltage amplitude and phase, and performing the synchronization process until the voltage amplitude and phase are fully synchronized.

[0027] Furthermore, the control calculation formula for the synchronization control module is as follows: Δu=UA_converter2−UA_converter1=U2cos(ω2t+φ2)−U1cos(ω1t+φ1)

[0028] Here, Δu denotes the instantaneous difference between the output voltages of the second converter and the first converter, U A_converter1 denotes the output voltage of the first converter, U A_converter2 denotes the output voltage of the second converter, U1 and U2 each denote the voltage amplitudes of the output sides of the two converters, ω1 and ω2 each denote the angular frequencies of the output sides of the two converters, and φ1 and φ2 each denote the initial phase angles of the output sides of the two converters;

[0029] The control formula for the synchronization process is: Δu=UA_converter2−UA_converter1≈−2Umsin(ω2+ω12t+φ2+φ12)sin(ω2−ω12t+φ2−φ12)

[0030] By regulating the phase difference and the amplitude difference, voltage synchronization between the two converters is achieved step by step.

[0031] To achieve the aforementioned objectives, the present invention provides, in a second aspect, an electronic device comprising a processor and a memory, wherein the processor is configured to implement the steps of the control method for constructing a hybrid AC / DC microgrid with photovoltaics, energy storage and charging when executing a computer program stored in memory.

[0032] To achieve the above-mentioned objectives, the present invention provides in a third aspect a computer-readable storage medium on which a computer program is stored which, when executed by a processor, performs the steps of the control method for constructing a hybrid AC / DC microgrid with photovoltaics, energy storage and charging.

[0033] The present invention has the following advantageous effects: In comparison to the prior art, the present invention provides a control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging, a device and a medium that effectively solves the problem of system instability caused by frequency and voltage fluctuations when switching the microgrid from grid-connected to island operation, based on a dynamic coordinated control mechanism between the energy storage device, the photovoltaic system and the electric vehicle. In particular, the present invention uses a classification based on the state of charge (SOC) values ​​of the energy storage devices.This allows the operating modes of the energy storage devices to be gradually adapted to switch from PQ mode to VSG mode in order to support the voltage and frequency of the microgrid. If energy storage devices and photovoltaic systems cannot fully meet the grid demand, electric vehicles are further integrated to feed power into the microgrid via charging stations. This creates a multi-stage, diversified power control mechanism that improves the system's adaptability. Furthermore, the present invention ensures seamless switching during the parallel operation of multiple devices through synchronous control technology, thereby reducing dependence on the external grid, improving the stability and autonomous control capability of the microgrid, lowering costs, and effectively addressing problems such as the instability of photovoltaic power generation. BRIEF DESCRIPTION OF THE DRAWING

[0034] In order to illustrate the technical solutions in the embodiments of the present invention more clearly, the drawings required for the description of the embodiments are briefly presented below. Fig. Figure 1 shows a topology diagram of a hybrid AC / DC microgrid system with photovoltaics, energy storage and charging, as disclosed in an embodiment of the present invention. Fig. Figure 2 shows a flowchart of a micronetwork control system as disclosed in an embodiment of the present invention. Fig. Figure 3 shows a schematic structure diagram of a micronetwork control system as disclosed in an embodiment of the present invention. Fig. Figure 4 shows a flowchart for the classification of energy storage devices and the allocation of power, as disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] To enable experts in the technical field to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below with reference to the drawings of those embodiments. It is understood that the described embodiments represent only a subset of the embodiments of the present invention and not all of them. All other embodiments that experts in this field obtain from the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0036] Fig. Figure 1 shows the topology of an AC / DC microgrid system with photovoltaics, energy storage, and charging. The topology comprises two buses: a DC bus and an AC bus. The DC and AC buses are connected via a DC / AC converter, which operates in PQ mode. The AC bus is connected to the grid via a transformer. The hybrid AC / DC microgrid can switch between grid-connected and islanded operation. In grid-connected operation, all converters operate in PQ mode and control the allocation of active and reactive power. In islanded operation, at least one converter switches to VSG mode and simulates the behavior of a synchronous generator to provide virtual inertia and damping, thus supporting the voltage and frequency stability of the microgrid.

[0037] Virtual inertia and damping are key concepts in the control engineering of virtual synchronous generators (VSGs), which are used to emulate the characteristics of conventional rotating generators. This increases the stability of microgrids under frequency and voltage fluctuations.

[0038] It is understandable that conventional synchronous generators, through their rotating rotors, provide inertia and thus reduce frequency fluctuations during load changes. Virtual inertia simulates this property using the converter and enables power electronic devices (such as energy storage systems and photovoltaic inverters) to deliver a specific inertial response to changes in system frequency, similar to that of synchronous generators. In particular, virtual inertia allows the microgrid to provide a certain amount of power support during frequency drops. This slows down the frequency decay and helps restore grid stability.

[0039] Damping refers to the process of slowing down system oscillations by regulating power. Conventional synchronous generators produce damping through electromagnetic force, thus helping the grid to stabilize quickly during frequency fluctuations. The virtual synchronous generator simulates this damping effect by adjusting the output power (i.e., active power). This helps to reduce excessive oscillations in the system and restore the grid to a stable state. A damping response typically occurs when the grid frequency deviates from its nominal value and provides the necessary power correction to prevent excessive frequency drift.

[0040] In conventional power supply systems, synchronous generators regulate reactive power via the excitation electromotive potential to counteract fluctuations in the reactive load and thus maintain system voltage stability. In a virtual synchronous generator, voltage regulation and excitation control together form a reactive power-voltage control loop. By deriving a reference voltage from the synchronous generator's voltage regulation unit, the voltage droop control characteristic of the synchronous generator is realized. This ensures the reactive power balance and voltage stability in the power supply system, thereby guaranteeing a stable and high-quality power supply.

[0041] In summary, virtual inertia helps the system counteract frequency fluctuations and provide short-term support, while damping reduces frequency oscillations. The excitation control system actively regulates reactive power to maintain a stable voltage at the converter. Together, these mechanisms ensure the stable operation of the microgrid.

[0042] The energy storage module, the photovoltaic array, and the charging station are each connected to the AC bus via a DC / AC converter. The DC / AC converter operates in either PQ or VSG mode. Other voltage-matched AC loads are connected directly to the AC bus. A photovoltaic unit is connected to the AC bus via a unidirectional DC / DC converter and feeds in direct current. The energy storage module and the charging station are each connected to the AC bus via a bidirectional DC / DC converter. These bidirectional DC / DC converters enable charge and discharge control for both the energy storage system and the electric vehicle battery connected to the charging station. Additional voltage-matched DC loads are connected directly to the DC bus.This configuration allows the energy storage devices to provide power support when power demand is insufficient, while the charging station can simultaneously charge the electric vehicle or support the microgrid by feeding power back into the grid.

[0043] Furthermore, a photovoltaic power generation unit and a charging station unit are connected in the DC subsystem, allowing the entire DC subsystem to operate independently; the AC subsystem can also be operated independently. Based on the decentralized power supply capacity, the supply distance, and the load characteristics of the entire microgrid system, the voltage level of the AC bus is set at 400 V. Referring to various technical standards, engineering tests, and the voltage level of DC loads, the voltage level of the DC bus is set at 750 V. To ensure safe and stable system operation, the system's power supply and demand must always be balanced. This power balance is reflected in the bus voltage. If the bus voltage tends towards stability or remains constant, the system has achieved the power balance.The basic energy relationship is as follows: PPV+PBAT+PCAR+PL=0

[0044] Here, P denotes PV the discharge power of the photovoltaic unit, P BAT denotes the charging / discharging power of the energy storage unit (it is considered negative when the energy storage device is discharging, and positive when it is charging), P CAR denotes the charging / discharging power of the charging station unit (it is assumed to be negative when the electric vehicle battery is discharging, and positive when charging) and P L denotes the power consumption of other AC / DC loads.

[0045] According to the embodiments of the present invention, it should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system, for example, by means of a series of computer-executable instructions. Although a logical sequence is shown in the following procedure, the steps shown or described can, in certain cases, be carried out in a different order than that given here.

[0046] As in Fig. 2, Fig. 3 to Fig. As shown in Figure 4, the present invention provides a control method for constructing a hybrid AC / DC microgrid with photovoltaics, energy storage and charging, comprising the following steps: Step S100: Classify the energy storage converters based on the SOC values ​​of the energy storage devices from high to low, switch the operating mode of the energy storage converter with the highest priority from PQ mode to VSG mode; Step S200: Recording the voltage and frequency of the microgrid and determining whether the fluctuation range of the voltage and frequency of the microgrid exceeds the deadband range for the control; Step S300: Calculate, if the frequency fluctuation in the microgrid exceeds the deadband range for the control, the required active power compensation via the active power frequency control in VSG mode, and adjust the active power output of the microgrid and the energy storage devices; Step S400: Adjust, if the voltage fluctuation in the microgrid exceeds the deadband for control, the reactive power output of the microgrid and the energy storage devices via reactive power voltage control in VSG mode; Step S500: Acquire the SOC values ​​of the energy storage devices, adjust the operating modes of the energy storage devices stepwise in descending order of SOC values ​​and switch from PQ mode to VSG mode, synchronize, using a synchronization control module, the voltage amplitude and phase angle of this energy storage converter with those of the energy storage converters already operating in VSG mode, and stepwise support the voltage and frequency of the microgrid by the energy storage devices; Step S600: Switching on the photovoltaic devices on the AC bus in descending order of adjustable capacities, if all energy storage devices cannot respond to voltage and frequency fluctuations in the microgrid after switching to VSG mode; Step S700: Synchronize, before switching on the photovoltaic device, the voltage amplitude and phase angle of the DC / AC converter of the photovoltaic device with those of the already switched-on energy storage devices using the synchronization control module; Step S800: Switching the operating mode of the photovoltaic device from PQ mode to VSG mode in order to support the voltage and frequency of the microgrid together with the energy storage unit; Step S900: Adjusting the control algorithm for the charging station and building up the voltage of the microgrid by feeding power from electric vehicles into the microgrid, if it is still not possible to fully react to the voltage and frequency fluctuations of the microgrid; Step S1000: Synchronize, before switching on the electric vehicle, the voltage amplitude and phase of the electric vehicle's charging station using the synchronization control module with the voltage amplitude and phase angle of the already switched-on converters; Step S1100: Control, using the synchronization control module, the electric vehicle's battery to support the voltage and frequency of the microgrid together with the energy storage devices and the photovoltaic array.

[0047] In this embodiment, as described in steps S100 to S500 (first processing module) above, the energy storage converters (PCS) are classified from high to low according to the state of charge (SOC) of the energy storage devices, and the PCS with the highest priority switches its operating mode from priority (PQ) to variable speed (VSG). The voltage and frequency of the microgrid are monitored. If the voltage and frequency fluctuations of the microgrid exceed the deadband for control due to disturbances or load changes, the active and reactive power balancing required to achieve the system's target frequency is determined based on the current voltage and frequency of the microgrid.

[0048] In active power-frequency control in the VSG (Variable Gearbox Control), the relationship between active power and frequency is derived from the rotor characteristics of synchronous generators using the rotor motion equation. The formula for calculating the required active power to be compensated is as follows: P=Jω0dωdt+Dω0(ω−ω0)

[0049] Here, P denotes the active power compensation required for the system to reach the target frequency, J denotes the coefficient of inertia of the virtual synchronous generator, ω0 denotes the nominal angular frequency, and ω denotes the output angular frequency of the VSG. dωdt denotes the rate of change of the angular frequency and D denotes the damping coefficient of the virtual synchronous generator.

[0050] The grid-forming converter can provide virtual inertia and damping, thus providing voltage and frequency support for the microgrid. Virtual synchronous generator (VSG) control technology is a current transformer control technology that enables power electronic devices, such as flexible AC / DC transmission systems, renewable energy generation plants, electric vehicles, and energy storage systems, to simulate rotational inertia and damping characteristics similar to rotating electrical machines. In inertial response mode, the change in active power is: PIntertia=−TJfN×dfdt×PN

[0051] Here, P denotes Inertia the change in the active power of the microgrid during the inertial response, T J denotes the equivalent time constant of inertia, f N denotes the nominal frequency of the microgrid system dfdt denotes the frequency change rate of the micronetwork and P N denotes the nominal active power of the network-forming device.

[0052] The calculated change in active power is distributed to the respective inverters in order to regulate the inertial response.

[0053] The damping active power arises from oscillations between the voltage at the grid-forming system and the voltage of the internal voltage source. This active power is provided autonomously by the converter and can react within less than 5 milliseconds. The damping active power serves as a measure of the damping effect achievable by the energy storage system and is expressed as: PDamping=D(ω−ω0)

[0054] Here, P denotes DampingThe damping active power provided by the virtual synchronous generator, D denotes the damping coefficient of the virtual synchronous generator, ω0 denotes the nominal angular frequency and ω denotes the output angular frequency of the VSG.

[0055] Reactive power-voltage control simulates the control characteristics by mimicking the excitation process of a synchronous machine. The relationship between the converter's reactive power output and the voltage can be represented as follows: ΔU=Dq(Qref−Qe)+(Uref−U)

[0056] Here, ΔU denotes the change in voltage, D q denotes the reactive power droop coefficient, Q ref denotes the reactive power setpoint, Q e denotes the reactive power output of the converter, U ref denotes the voltage setpoint and U denotes the output voltage amplitude of the converter.

[0057] Based on the state of charge (SOC) of the energy storage devices, the voltage and frequency of the microgrid are supported in stages, thus resolving the balancing problem when multiple energy storage devices are connected in parallel. The specific workflow is as follows: The SOC of the energy storage devices is detected, the operating mode of the energy storage converter connected to the energy storage device with the highest SOC is switched from power factor (PQ) to variable voltage (VSG), and the AC bus voltage is built up to support the voltage and frequency of the microgrid. During this process, the other converters continue to operate in PQ mode. If the power of an energy storage device proves insufficient to support the voltage and frequency of the microgrid, the operating modes of the energy storage converters connected to these energy storage devices are switched in stages from PQ to VSG, in descending order of SOC.In this way, the energy storage devices can gradually support the voltage and frequency of the microgrid.

[0058] In this embodiment, as described in steps S600 to S800 (second processing module) above, if all energy storage devices of the microgrid still do not fully respond to frequency fluctuations of the microgrid after switching to VSG operation, the photovoltaic devices on the AC side are switched on in descending order of their adjustable capacities. Before switching on a photovoltaic device, the second synchronization control module performs voltage synchronization of the converter to synchronize the voltage amplitude and phase of the DC / AC converter connected to that photovoltaic device with those of the converters connected to the energy storage devices already switched on.The operating modes of the corresponding DC / AC converters are switched by PQ in VSG so that they, together with the energy storage units, can build up the AC bus voltage and thus support the voltage and frequency of the microgrid.

[0059] It is understandable that by gradually integrating photovoltaic devices and implementing voltage and phase synchronization, the photovoltaic system can work seamlessly with the energy storage units to provide additional voltage and frequency support. Switching the photovoltaic converter to virtual synchronous generator (VSG) mode simulates the inertia and damping characteristics of a virtual synchronous generator, thereby increasing the dynamic control capability of the microgrid. This allows the system to better counteract frequency fluctuations, reduces dependence on the external grid, and enhances the autonomous control and stability of the microgrid. This mechanism effectively improves the self-sustaining capability of the microgrid in islanded operation and ensures the stability and reliability of system operation.

[0060] In this embodiment, as described in steps S900-51100 (third processing module) above, the control algorithm for the charging stations on the AC bus side is adapted when the photovoltaic array generates no or insufficient current due to darkness or shade, and thus all energy storage devices and the photovoltaic devices cannot yet react to voltage and frequency fluctuations of the microgrid after being switched on. Electric vehicles feed current into the microgrid via the charging stations to establish a bus voltage for the microgrid. The operating mode of the corresponding DC / AC converter is switched from PQ to VSG, and its voltage amplitude and phase angle are synchronized with those of the converters already switched on by means of a third synchronization control module.In this way, the batteries of the electric vehicles, together with the energy storage devices and the photovoltaic array, can provide the independent microgrid with short-term frequency and voltage support.

[0061] Fig. Figure 4 shows a flowchart for the classification of energy storage devices and the allocation of power. As in Fig. As shown in section 4, the specific steps for classifying energy storage devices based on their charge states and for allocating power to respond to frequency fluctuations in the microgrid are as follows: 1) Recording the SOC values ​​of the respective energy storage devices; 2) Sorting the SOC values ​​of the energy storage devices and setting the priorities of the respective energy storage devices to respond to fluctuations in the microgrid based on the SOC values ​​in descending order; 3) Distribute the power required for voltage and frequency regulation sequentially to the respective energy storage devices according to their priorities and in combination with their maximum charge / discharge power, until the power allocation is complete. The individual steps are as follows: 3.1) Initializing the power required to respond to frequency and voltage fluctuations in the microgrid, i.e., the power to be allocated; 3.2) Iterating through the respective energy storage devices and selecting the PCS of the energy storage device with the highest priority as the current PCS, wherein, if the maximum charge / discharge power of the current PCS is less than the power to be allocated, setting the maximum charge / discharge power of the current PCS as the charge / discharge power of the current PCS and subtracting the charge / discharge power of the current PCS from the power to be allocated to obtain the new power to be allocated; otherwise, setting the power to be allocated as the charge / discharge power of the current PCS; 3.3) Determine if all PCS have been traversed, if the traversal is incomplete, proceed to step 3.2), otherwise determine that the control capability of the energy storage unit has reached its saturation limit, exit and close.

[0062] The steps outlined above ensure that the energy storage system can effectively respond to frequency and voltage fluctuations in the microgrid by dynamically allocating control power based on the state-of-charge (SOC) values ​​of the energy storage devices. By allocating power starting with the energy storage device with a higher SOC, the device in a better state is prioritized for control. This optimizes the utilization efficiency of the energy storage resources. This method balances the load on the individual energy storage units, preventing excessive discharge or charge of specific devices and thus extending their lifespan. Simultaneously, the microgrid can respond quickly to frequency or voltage fluctuations, ensuring the system's stability and reliability.When the energy storage device's control capacity reaches its saturation limit, the system can immediately interrupt the power supply. This prevents overloading and ensures the safe operation of the system.

[0063] In this embodiment, the control process of the synchronization control module comprises the following: In VSG operating mode, the converter exhibits a voltage source characteristic. Therefore, starting with the second converter device, a synchronous parallel connection must be established by the synchronization control module before a new device is connected. This ensures that the voltage of the transducer connected to the device is fully synchronized with that of the transducer already operating in VSG mode. This enables a "zero" impact. Using the synchronization control as an example before connecting the second transducer with the VSG characteristic, the synchronization control module is implemented as follows:

[0064] Using phase A as an example, the output voltage U is A_converter2 of the second converter, which will soon be connected to the microgrid for voltage support, and the output voltage U A_converter1 of the first converter that has already been switched on, in each case: UA_converter2=U2cos(ω2t+φ2) UA_converter1=U1cos(ω1t+φ1)

[0065] Here, U denotes A_converter1 the output voltage of the first converter, U A_converter2denotes the output voltage of the second converter, U1 and U2 denote the voltage amplitudes of the output sides of the two converters, ω1 and ω2 denote the angular frequencies of the output sides of the two converters, and φ1 and φ2 denote the initial phase angles of the output sides of the two converters.

[0066] The instantaneous difference between the output voltages of the two converters is: Δu=UA_converter2−UA_converter1=U2cos(ω2t+φ2)−U1cos(ω1t+φ1)

[0067] Here, Δu denotes the instantaneous difference between the output voltages of the second converter and the first converter. To achieve Δu = 0, the following specific steps are required:

[0068] By controlling the magnitude of U2 so that it corresponds to the voltage amplitude U1 of the first converter U1, i.e., U2=U1=U m The instantaneous voltage difference can then be simplified to: Δu=UA_converter2−UA_converter1≈−2Umsin(ω2+ω12t+φ2+φ12)sin(ω2−ω12t+φ2−φ12)

[0069] From the above formula (4) it can be seen that by the control, such that sin(ω2−ω12t+φ2−φ12)=0, i.e. ω1=ω2 and φ1=φ2, so by matching the angular frequency and the phase of the output voltages of the two converters, the instantaneous voltage difference Δu = 0 can be achieved.

[0070] By controlling the amplitude and phase of the second converter's output voltage so that they match the amplitude and phase of the first converter's output voltage, the second converter can be connected to the microgrid without any spurious input. Upon receiving the PQ-to-VSG command, the second converter's output voltage amplitude and phase are adjusted in real time. The individual steps are as follows: 1) After determining the voltage phase φ2 and reference amplitude U* of the output side of the second converter, as well as the voltage phase φ1 and amplitude U out_converter1 The output side of the first converter, determined using the VSG algorithm, is processed according to formula (5) to calculate Δφ, Δφ, ΔU, U ref_converter and φ, where the initial values ​​of dφ and dU are set to 0; {φ=φ2+dφUref_converter2=U*+dUΔφ=φ−φ1ΔU=Uref_converter2−Uout_converter1

[0071] Here, dφ denotes the cumulative value of the phase-controlled step size, dU denotes the cumulative value of the amplitude-controlled step size, U ref_converter2 denotes the reference voltage amplitude of the output side of the second converter, Δφ denotes the voltage phase difference between the two converters, ΔU denotes the voltage amplitude difference between the two converters, and U out_converter1 denotes the output voltage amplitude of the first converter.

[0072] 2) Determining the values ​​of the sign variables var1 and var2 based on the magnitudes of Δφ and ΔU to clarify the direction of the control, and rules dφ and dU according to formula (6); {dφ=dφ2−var1⋅step_φdφ2=dφdU=dU2−var2⋅step_UdU2=dU

[0073] Here, var1 and var2 denote sign variables that take the values ​​1, -1 or 0; step_φ denotes the phase control step size; and step_U denotes the voltage control step size.

[0074] 3) The values ​​of Δφ and ΔU are determined cyclically. The synchronization process is considered complete when ΔU falls below the amplitude difference threshold and Δφ falls below the phase difference threshold.

[0075] The operation of the aforementioned synchronization control modules ensures that multiple converters in VSG mode achieve complete voltage amplitude and phase matching when connected to the microgrid. This enables synchronous grid connection operation with zero spurious voltage. In this process, the voltage amplitude and phase of the second converter are adjusted in real time to synchronize with the voltage of the already connected converter. This prevents system fluctuations or surge loads caused by voltage mismatch.This method not only increases the stability of the microgrid system, but also avoids sudden voltage fluctuations when connecting the converter to the grid, thus ensuring the safety and reliability of the microgrid, especially the coordinated operating effect when decentralized energy sources such as energy storage devices and photovoltaics jointly regulate the system frequency and voltage.

[0076] In summary, the control method proposed by the present invention for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage, and charging can dynamically adjust the number of connected energy storage devices, photovoltaic panels, and electric vehicles based on frequency fluctuations in the microgrid during the transition from grid-connected to island operation. This enables the rapid establishment of an AC bus to support the voltage and frequency of the microgrid, thus ensuring its operational stability. This reduces the dependence of conventional microgrids on the external grid and increases the autonomous control capability of the system.The scaling of energy storage devices in the microgrid is reduced by temporarily supporting the voltage and frequency of the microgrid through the power feed-in from electric vehicles, thereby lowering the cost of the microgrid. According to another aspect of the embodiments of the present application, an electronic device is provided comprising a processor and a memory, wherein the processor is configured to implement the steps of the method when executing a computer program stored in memory.

[0077] In the aforementioned embodiments of the present invention, the focus of the description of each embodiment is on different aspects. For parts that are not described in detail in a particular embodiment, reference can be made to the corresponding descriptions in other embodiments.

[0078] With regard to some of the embodiments provided in the present application, it should be understood that the disclosed technical content can be implemented in other ways. The embodiments of the devices described above serve only for illustration. The division of units may, for example, represent a logical division of functions. In actual implementation, other divisions may occur—for example, several units or components may be combined or integrated into another system, or some features may be ignored or omitted. Furthermore, the mutual couplings or direct couplings or communication links shown or discussed may be indirect couplings or communication links via specific interfaces, units, or modules, and may be in electrical or other form.

[0079] Furthermore, in the individual embodiments of the present invention, the functional units can be integrated into a single processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The aforementioned integrated unit can be implemented either in the form of hardware or in the form of a software functional unit.

[0080] If the integrated unit is implemented as a software functional unit and sold or used as a standalone product, it can be stored on a computer-readable storage medium. Based on this understanding, the technical solutions of the present invention can be substantially, or the parts that contribute to the prior art, or all or part of the technical solutions embodied in the form of a software product. This computer software product is stored on a storage medium and contains several instructions that cause a computer device (e.g., a PC, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention.The aforementioned storage media include: USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks or optical media, and other media capable of storing program code.

[0081] The foregoing description merely presents preferred embodiments of the present invention. It should be noted that numerous improvements and modifications can be made by those skilled in the art without departing from the principles of the present invention, and that such improvements and modifications are also to be regarded as falling within the scope of protection of the present invention. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 118232365A

[0003]

Claims

A control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage, and charging, characterized in that it comprises the following steps: classifying the energy storage converters from high to low based on the SOC values ​​of the energy storage devices; switching the operating mode of the energy storage converter with the highest priority from PQ mode to VSG mode; acquiring the voltage and frequency of the microgrid and determining whether the voltage and frequency fluctuation range of the microgrid exceeds the deadband for control; calculating, if the frequency fluctuation in the microgrid exceeds the deadband for control, the required active power balancing via active power frequency control in VSG mode and adjusting the active power output of the microgrid and the energy storage devices;Adjusting, if the voltage fluctuation in the microgrid exceeds the deadband for control, the reactive power output of the microgrid and the energy storage devices via reactive power voltage control in VSG mode; acquiring the SOC values ​​of the energy storage devices, adjusting the operating modes of the energy storage devices stepwise in descending order of SOC values ​​and switching from PQ mode to VSG mode, synchronizing, using a synchronization control module, the voltage amplitude and phase angle of this energy storage converter with those of the energy storage converters already operating in VSG mode, and stepwise supporting the voltage and frequency of the microgrid by the energy storage devices;Connecting the photovoltaic devices to the AC bus in descending order of adjustable capacities if all energy storage devices cannot respond to voltage and frequency fluctuations in the microgrid after switching to VSG mode; Synchronizing, before connecting the photovoltaic device, the voltage amplitude and phase angle of the DC / AC converter of the photovoltaic device with those of the already connected energy storage devices using the synchronization control module; Switching the operating mode of the photovoltaic device from PQ mode to VSG mode in order to support the voltage and frequency of the microgrid together with the energy storage unit;Adapting the control algorithm for the charging station and building up the microgrid voltage by feeding power from electric vehicles into the microgrid, if it is still not possible to fully respond to voltage and frequency fluctuations in the microgrid; Synchronizing, before connecting the electric vehicle, the voltage amplitude and phase of the electric vehicle charging station with the voltage amplitude and phase angle of the already connected energy storage converters using the synchronization control module; Controlling, using the synchronization control module, the electric vehicle battery to support the voltage and frequency of the microgrid together with the energy storage devices and the photovoltaic array. A control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to claim 1, characterized in that the method for classifying the energy storage converters based on the SOC values ​​of the energy storage devices from high to low comprises the following: acquiring the SOC values ​​of the respective energy storage devices; sorting the SOC values ​​of the energy storage devices and setting the priorities of the respective energy storage devices to respond to fluctuations in the microgrid based on the SOC values ​​in descending order; distributing the power required for control to the respective energy storage devices in sequential order and allocating the power based on the priority and the maximum charge / discharge power until the power allocation is completed. Control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to claim 2, characterized in that the method for distributing the power required for control to the respective energy storage devices in sequential order and allocating the power according to the priority and the maximum charging / discharging power, until the power allocation is completed, comprises the following: initializing the power to be allocated which is required to respond to frequency and voltage fluctuations in the microgrid;Iterate through the respective energy storage devices and select the PCS of the energy storage device with the highest priority as the current PCS, wherein, if the maximum charge / discharge power of the current PCS is less than the power to be allocated, set the maximum charge / discharge power of the current PCS as the charge / discharge power of the current PCS and subtract the charge / discharge power of the current PCS from the power to be allocated to obtain the new power to be allocated; otherwise, set the power to be allocated as the charge / discharge power of the current PCS; determine whether all PCS have been traversed, wherein, if the traversal is incomplete, proceed to the previous step, otherwise, determine that the controllability of the energy storage unit has reached its saturation limit, exit, and close. Control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to claim 1, characterized in that the active power frequency control in VSG mode calculates the required active power compensation based on the rotor properties of synchronous generators using the rotor motion equation, wherein the exact calculation formula is as follows: P = J ω 0 d ω dt + D ω 0 ( ω − ω 0 ) where P denotes the active power compensation required for the system to reach the target frequency, J denotes the coefficient of inertia of the virtual synchronous generator, ω 0 denotes the nominal angular frequency, ω denotes the output angular frequency of the VSG, d ω dt denotes the rate of change of the angular frequency and D denotes the damping coefficient of the virtual synchronous generator. Control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to claim 1, characterized in that the calculation formula for the change in active power due to the inertial reaction in VSG mode is: PI nertia = − TJ f N × dfdt × PN P Inertia T denotes the change in the active power of the microgrid during the inertial response. J denotes the equivalent time constant of inertia, f N the nominal frequency of the microgrid system, dfdt denotes the frequency change rate of the micronetwork and P N denotes the nominal active power of the network-forming device. The formula for calculating the damping power in VSG mode is: PD amping = D ( ω − ω 0 ) P Damping denotes the damping active power provided by the virtual synchronous generator, D denotes the damping coefficient of the virtual synchronous generator, ω 0 denotes the nominal angular frequency and ω denotes the output angular frequency of the VSG. Control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to claim 1, characterized in that the calculation formula for the reactive power-voltage control in VSG mode is: Δ U = D q ( Q ref − Q e ) + ( U ref − U ) where ΔU denotes the change in voltage, D q denoted as the reactive power droop coefficient, Q ref denoted as the reactive power setpoint, Q e denotes the reactive power output of the converter, U ref denotes the voltage setpoint and U denotes the output voltage amplitude of the converter. A control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to claim 1, characterized in that the control steps of the synchronization control module are as follows: controlling, using the synchronization control module, the voltage amplitude and phase of the energy storage device, the photovoltaic device or the converter of the charging station for electric vehicles, such that it corresponds to the voltage amplitude and phase of the already connected VSG converters, thereby ensuring that the instantaneous voltage values ​​have a difference of zero when the respective converters are operated in parallel in VSG mode; adjusting the phase control step size and amplitude control step size based on the differences in the voltage amplitude and phase and performing the synchronization process until the voltage amplitude and phase are fully synchronized. Control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to claim 7, characterized in that the control calculation formula for the synchronization control module is as follows: Δu = UA_converter2 − UA_converter1 = U2 cos(ω2t + φ2) − U1 cos(ω1t + φ1) where Δu denotes the instantaneous difference between the output voltages of the second converter and the first converter, U A_converter1 denotes the output voltage of the first converter, U A_converter2 denotes the output voltage of the second converter, U 1 and U 2 denote the voltage amplitudes of the output sides of the two converters, ω 1 and ω 2 denote the angular frequencies of the output sides of the two converters, and φ 1 and φ 2 to denote the initial phase angles of the output sides of the two converters; The control formula for the synchronization process is: Δu = UA_converter2 − UA_converter1 ≈ −2 U msin ( ω 2 + ω 1 2 t + φ 2 + φ 1 2 ) sin ( ω 2 − ω 1 2 t + φ 2 − φ 1 2 ) Voltage synchronization between the two converters is achieved gradually by regulating the phase difference and the amplitude difference. Electronic device characterized in that it comprises a processor and a memory, wherein the processor is configured to implement, when executing a computer program stored in memory, the steps of the control method for constructing a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to one of claims 1 to 8. A computer-readable storage medium on which a computer program is stored, characterized in that the computer program, when executed by a processor, performs the steps of the control method for setting up a hybrid AC / DC microgrid with photovoltaics, energy storage and charging according to one of claims 1 to 8.

Images