A solid-state microgrid system and control method thereof

Abstract

The present invention relates to a solid-state microgrid system and a control method thereof, wherein the solid-state microgrid system comprises: a DC bus connected to a DC bus port; a DC power unit, which adopts a modular design, an input side connected to a DC port, and an output side connected to the DC bus; an AC power unit, which adopts a modular design, a DC side connected to the DC bus, and an AC side connected to an AC port; and a coordination control unit, which is respectively connected to the DC power unit and the AC power unit, for realizing energy access, conversion, distribution, control and management. The present invention can efficiently integrate different types of energy and loads.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and particularly to a solid-state microgrid system and a control method thereof. Background Art

[0002] Due to the intensification of the global energy crisis, people's concerns about fuel depletion, power shortage, and global warming are increasing. Clean and renewable solar and wind energy provide solutions to these problems through distributed generation. As an important interface for connecting the electric energy generated by distributed power sources mainly based on renewable energy to the power system, the microgrid has become a research hotspot.

[0003] With the increasing demand for intensification and miniaturization of energy supply, and the rapid development of power electronics technology, especially new high-power semiconductor devices such as silicon carbide, it has laid a foundation for the further development of the microgrid towards power electronics. Under the traditional power transmission and distribution system structure, the microgrid needs to be equipped with corresponding power electronic converters for new energy power generation equipment, energy sources, energy storage systems, and loads respectively to achieve functions such as AC-DC conversion of voltage, local load power supply, and grid connection. The traditional method of using multiple power converters for each distributed device brings challenges, including increased costs, reduced system power density, and complex communication between power converters. In addition, the hierarchical control method of the traditional power transmission and distribution structure leads to complex scheduling management, unable to make full use of the rapidity of power electronic converters to quickly respond to grid and load fluctuations.

[0004] Therefore, it has important development prospects to replace the traditional power distribution system through more flexible and intelligent integration and multi-port design of microgrid converter devices. The emergence of power conversion technologies such as dual-active-bridge DC transformers, multi-port converters, and solid-state transformers has laid a foundation for the integrated development of microgrid systems. However, the above microgrid technologies only focus on the research from the perspective of the individual topology or control method of the converter, while the actual microgrid needs to provide an integrated platform for distributed power generation equipment, energy storage equipment, loads, and user terminals, and realize functions such as energy management and transmission control, voltage level conversion, electrical isolation, reactive power compensation, and real-time control. System-level microgrid control is crucial for the stable operation of new energy equipment, so it is also an urgent problem to be solved in the integration of microgrids.

[0005] The existing publicly disclosed patent document CN109728581A discloses a composite energy router and a control method. However, this composite energy router is essentially composed of multiple independent power distribution systems directly connected through conventional devices such as power frequency transformers and circuit breakers. It lacks modular and integrated ports, resulting in problems such as low power density and large equipment volume. In terms of control, this solution only focuses on discussing the control of the grid-side converter for the DC bus voltage and harmonic distortion rate, without discussing the operation and control scheme of the core of the energy router - the power electronic solid-state transformer, nor discussing how the energy router realizes internal energy management, distribution, monitoring, and protection. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a solid-state microgrid system and its control method, which can efficiently integrate different types of energy sources and loads.

[0007] The technical solution adopted by the present invention to solve its technical problems is to provide a solid-state microgrid system, including:

[0008] A DC bus connected to a DC bus port; the DC bus port is used to connect a DC load.

[0009] A DC power unit, designed modularly, with its input side connected to a DC port and its output side connected to the DC bus; the DC port is used to connect a distributed energy storage device.

[0010] An AC power unit, designed modularly, with its DC side connected to the DC bus and its AC side connected to an AC port; the AC port is used to connect to an AC grid.

[0011] A coordinated control unit, connected to the DC power unit and the AC power unit respectively, for realizing at least one of energy access, conversion, distribution, control, and management.

[0012] The DC power unit includes:

[0013] A sampling circuit part for sampling the voltage and current of the DC port and the voltage and current of the DC bus.

[0014] A main circuit part, adopting a DC / DC structure that can realize bidirectional energy flow and has high-frequency isolation.

[0015] A control circuit part for identifying the inserted device on the DC port side, transmitting the identification result to the coordinated control unit, and controlling the operation state of the main circuit part according to the control strategy of the DC power unit issued by the coordinated control unit.

[0016] The coordination control unit is further configured to determine the control strategy of the DC power unit according to the identification result of the insertion device on the DC port side.

[0017] The control strategy of the DC power unit includes a DC port voltage control mode, a DC bus voltage control mode, and a power control mode; in the DC port voltage control mode, the DC bus voltage is uncontrolled, the DC port voltage is controlled, and the power flow direction and magnitude are determined by the load; in the DC bus voltage control mode, the DC port voltage is uncontrolled, the DC bus voltage is controlled, and the power flow direction and magnitude are determined by the load; in the power control mode, both the DC bus voltage and the DC port voltage are uncontrolled, and only the magnitude and direction of the power flow are controlled.

[0018] When the control strategy of the DC power unit received by the control circuit part is the DC port voltage control mode, the DC port current reference value is obtained through closed-loop control according to the desired voltage value of the DC port and the voltage of the DC port obtained by the sampling circuit part, and then the DC port preliminary current control value is obtained through closed-loop control according to the DC port current reference value and the current of the DC port obtained by the sampling circuit part, and then the DC port preliminary current control value is limited in current to obtain the DC port final current control value; the control quantity is optimized according to the current working condition of the main circuit part;

[0019] When the control strategy of the DC power unit received by the control circuit part is the DC bus voltage control mode, the DC bus current reference value is obtained through closed-loop control according to the expected value of the DC bus voltage and the voltage of the DC bus obtained by the sampling circuit part, and then the bus voltage preliminary current control value is obtained through closed-loop control according to the DC bus current reference value and the current of the DC bus obtained by the sampling circuit part, and then the bus voltage preliminary current control value is limited in current to obtain the bus voltage final current control value; the control quantity is optimized according to the current working condition of the main circuit part;

[0020] When the control strategy of the DC power unit received by the control circuit part is the power control mode, the expected current value is obtained according to the expected value of the DC bus power, and the actual current value is dynamically tracked to the expected current value through closed-loop control; the control quantity is optimized according to the current working condition of the main circuit part.

[0021] The AC power unit includes:

[0022] A detection circuit part for detecting three-phase grid line voltages and phase currents, DC bus voltages and currents, output voltages and currents;

[0023] A drive circuit part adopting a three-phase two-level converter structure or a CHB multilevel converter structure with a common DC bus;

[0024] The main control part is used to determine the control method of the drive circuit part according to the DC bus voltage control mode issued by the coordination control unit.

[0025] The main control part includes:

[0026] The first control sub-unit is used to control the drive circuit part by constant voltage or constant power in grid-connected or off-grid mode when the DC bus is controlled by the energy storage unit;

[0027] The second control sub-unit is used to control the drive circuit part to operate in the networking mode when the DC bus is connected to the grid through the control inverter.

[0028] When the first control sub-unit controls the drive circuit part by constant voltage or constant power in grid-connected or off-grid mode, it obtains the three-phase grid line voltage V detected by the detection circuit part pabc , and transforms the three-phase grid line voltage V pabc into the voltage V pd and V pq in the two-phase rotating coordinate system through coordinate transformation. The q-axis voltage signal V pq is input into the PI controller to obtain the system real-time angular frequency deviation signal ω err . The system real-time angular frequency deviation signal ω err and the rated angular frequency signal ω 0 are added to obtain the real-time angular frequency signal ω. The real-time angular frequency signal ω passes through an integration link to obtain the phase angle signal reference θ pll ;

[0029] When the first control sub-unit controls the drive circuit part by constant voltage or constant power in grid-connected or off-grid mode, according to the collected three-phase grid line voltage V pabc and phase current i abc , it uses the phase angle signal reference of the system to perform coordinate transformation to transform the three-phase grid line voltage V pabc into the voltage amplitude signal in the two-phase rotating coordinate system; the phase current i abc in the three-phase stationary coordinate system is transformed into the current signals I d and I q in the two-phase rotating coordinate system;

[0030] When the first control sub-unit controls the drive circuit part by constant voltage or constant power in grid-connected or off-grid mode, according to the DC bus voltage rated value U dcref and the DC bus voltage U detected by the detection circuit part dc , the difference between the two is obtained to get the first deviation signal. The first deviation signal is input into the DC bus voltage controller to obtain the d-axis current reference signal i dref; According to the reactive power demand of the power grid system, a reactive power control link is introduced, and the reactive power reference value Q ref and the actual output value Q e are subtracted to obtain a second deviation signal, and the second deviation signal is input into the reactive power controller to obtain the q-axis current reference signal i qref .

[0031] When the second control sub-unit controls the driving circuit part to operate in the networking mode, according to the rated value U of the DC bus voltage dcref and the DC bus voltage U detected by the detection circuit part dc , the two are subtracted to obtain a first deviation signal, and the first deviation signal is input into the DC bus voltage controller; the power grid voltage frequency deviation is input into the synchronous generator speed governor; based on the output of the DC bus voltage controller and the output of the synchronous generator speed governor, the active power setting value P ref is obtained, and the deviation between the active power setting value P ref and the actual output value P e is input into the synchronous machine rotor swing equation to obtain the power synchronizer angular frequency deviation signal Δω, and the power synchronizer angular frequency deviation signal Δω and the rated angular frequency signal ω 0 are added to obtain the system real-time angular frequency signal ω, and finally the phase angle signal reference θ vsg is obtained through the integrator; the deviation between the real-time voltage amplitude U of the grid connection point measured at the grid connection point pf and the rated value U of the grid connection point voltage N is input into the droop controller to generate a reactive power regulation deviation signal, and a power synchronous output voltage reference value is generated through the reactive power loop; based on the power synchronous output voltage reference value, coordinate transformation is performed using the phase angle signal reference to obtain the output voltage reference values V dref and V qref , and are input into the power synchronous output voltage closed loop to obtain the d-axis current reference value i dref and the q-axis current reference value i qref ; According to the d-axis current reference value i dref , the q-axis current reference value i qref respectively and the actual d-axis current i d and the q-axis current i qCompare to obtain the d-axis error signal and q-axis error signal, and respectively use PI controllers for closed-loop control of the d-axis error signal and q-axis error signal to obtain the adjusted voltage on the output filter inductor. By superimposing it with the grid connection point feedforward voltage, the output modulation voltage is generated. According to the phase information, inverse coordinate transformation is performed to obtain the modulation voltage in the two-phase stationary coordinate system; input the modulation voltage in the two-phase stationary coordinate system into the Space Vector Pulse Width Modulation (SVPWM) module for processing to obtain the drive signal of the drive circuit part.

[0032] The technical solution adopted by the present invention to solve its technical problems is to provide a control method for the above-mentioned solid-state microgrid system, including device-level control, where the device-level control refers to completing the control objectives for the AC power unit and DC power unit of the physical layer of the solid-state microgrid based on control information.

[0033] The control method of the solid-state microgrid system further includes system-level control, and the purpose of the system-level control is to provide an interface for the upper-level power grid.

[0034] Beneficial effects:

[0035] Due to the adoption of the above technical solution, compared with the prior art, the present invention has the following advantages and positive effects: To adapt to the access of various energy sources, loads, and energy storage devices, the present invention provides great flexibility and scalability through modularized AC / DC units and diverse interfaces, efficiently integrates different types of energy and loads, and enhances the interface adaptability. To ensure the stable operation and flexible control of the solid-state microgrid system, the present invention adopts an overall control method of hybrid collaborative control. Through the interaction between the main controller and the state information and operating conditions of each unit, it intelligently identifies the port devices and adjusts the operating modes and output powers of each sub-unit to adapt to different application scenarios. At the same time, intelligent microgrid control algorithms such as fault protection, grid connection / disconnection control, and power quality management are embedded to achieve the cross-level integration of the system, thus having the advantages of high adaptability and high reliability. Description of the drawings

[0036] Figure 1 is a schematic structural diagram of the solid-state microgrid system in the embodiment of the present invention;

[0037] Figure 2 is a schematic diagram of the control strategy of the DC power unit in the embodiment of the present invention;

[0038] Figure 3 is the control structure diagram of the AC power unit in the embodiment of the present invention;

[0039] Figure 4It is the adaptive collaborative control integration diagram of the control method for the solid-state microgrid system in the embodiment of the present invention. Specific Embodiment

[0040] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0041] The first embodiment of the present invention relates to a solid-state microgrid system, as Figure 1 shown, including:

[0042] A DC bus connected to the DC bus port; the DC bus port is used to connect a DC load;

[0043] A DC power unit, designed modularly, with its input side connected to the DC port and its output side connected to the DC bus; the DC port is used to connect a distributed energy storage device;

[0044] An AC power unit, designed modularly, with its DC side connected to the DC bus and its AC side connected to the AC port; the AC port is used to connect to the AC grid;

[0045] A coordinated control unit, connected to the DC power unit and the AC power unit respectively, for realizing at least one of energy access, conversion, distribution, control, and management.

[0046] This solid-state microgrid system adopts an integrated design of components such as an AC power unit, a DC power unit, a DC bus, an AC bus, and coordinated control. Magnetic integration is carried out for the filter inductor and the transformer to optimize the system performance and reduce the overall cost. Through the topological structure of sharing magnetic components, such as designing a common-mode inductor or adopting multi-layer PCB technology, the magnetic components of different inductors and transformers are shared between vertical layers, thereby reducing the system volume. Consider selecting integrated magnetic materials, such as soft magnetic sheets or magnetic nanomaterials, to improve the magnetic integration degree. In addition, by adopting a compact physical layout, packaging technology, and adaptive inductor design, multiple magnetic components can coexist efficiently. The solid-state microgrid integrates the output of the DC power unit and the output of the AC power unit. The AC-DC hybrid design reduces the redundant AC and DC bus structures caused by the traditional power transmission and distribution structure; through the use of new power devices for system integration and coordinated control between the system and modules, the integrated functions of energy access, conversion, distribution, control, and management are realized.

[0047] The DC power unit in this embodiment includes: a sampling circuit part for sampling the voltage and current of the DC port and the voltage and current of the DC bus; a main circuit part adopting a DC / DC structure capable of realizing bidirectional energy flow and having high-frequency isolation; and a control circuit part for identifying the inserted device on the DC port side, transmitting the identification result to the coordination control unit, and controlling the operating state of the main circuit part according to the control strategy of the DC power unit issued by the coordination control unit.

[0048] The main circuit part adopts a DC / DC structure that can realize bidirectional energy flow and has high-frequency isolation at the same time. The input interface can be flexibly connected to devices such as photovoltaic, wind power generation, and energy storage, and the input voltage control strategy can be selected according to the intelligent interface identification. It can realize the selection of maximum power tracking, power-limited operation and other modes for new energy power generation equipment, and at the same time can realize the charge and discharge and energy management control of energy storage equipment. The output side of the DC power unit is connected to the DC bus of the solid-state microgrid system, and the DC bus interface can be directly connected to the DC distribution network to realize the power transmission between the solid-state microgrid system and the DC system, so as to provide a household DC output interface and a high-voltage DC output interface. The number of DC power unit modules can be flexibly configured according to the capacity requirements of the solid-state microgrid system, without complex wiring and communication.

[0049] In this embodiment, it is defined that the energy flowing into the solid-state microgrid by the DC power unit is in the forward operation, and vice versa is in the reverse operation. Without considering the specific instructions of the top-level control and management unit, only from the final action response of the DC power unit, six scenarios can be obtained: 1. The DC power unit changes from stopped to started; 2. The DC power unit operates in forward boost; 3. The DC power operates in forward buck; 4. The DC power unit operates in reverse boost; 5. The DC power unit operates in reverse buck; 6. The DC power unit changes from running to stopped. The working principles of the DC power unit in each scenario will be introduced below.

[0050] 1) The DC power unit changes from stopped to started

[0051] Before the DC power unit operates, the coordination control unit should set different control strategies according to different plug-in devices. Generally speaking, there are three typical control strategies: ① DC port voltage control mode. The DC bus voltage is uncontrolled, the DC port voltage is controlled, and the power flow direction and magnitude are determined by the load; ② DC bus voltage control mode. The DC port voltage is uncontrolled, the DC bus voltage is controlled, and the power flow direction and magnitude are determined by the load; ③ Power control mode. Both the DC bus voltage and the DC port voltage are uncontrolled, and the converter controls the magnitude and direction of the power flow.

[0052] In this embodiment, appropriate control strategies can be selected according to different control modes, which can be divided into the following several types:

[0053] DC port voltage control mode: The DC port voltage outer loop and current inner loop control mode shall be adopted. As shown in (a) of Figure 2 , the DC port current reference value is obtained through PI control based on the expected voltage value of the DC port and the voltage of the DC port obtained by the sampling circuit part. Then, the preliminary DC port current control value is obtained through PI control based on the DC port current reference value and the current of the DC port obtained by the sampling circuit part. Then, the preliminary DC port current control value is limited by current to obtain the final DC port current control value. At this time, the DC port voltage expected value is given by the system, and the DC power unit needs to dynamically track the given value according to the current DC port voltage output value, and at the same time achieve current limiting.

[0054] DC bus voltage control mode: The DC bus voltage outer loop and current inner loop control mode shall be adopted. As shown in (b) of Figure 2 , the DC bus current reference value is obtained through PI control based on the expected DC bus voltage value and the voltage of the DC bus obtained by the sampling circuit part. Then, the preliminary bus voltage current control value is obtained through PI control based on the DC bus current reference value and the current of the DC bus obtained by the sampling circuit part. Then, the preliminary bus voltage current control value is limited by current to obtain the final bus voltage current control value. At this time, the DC bus voltage expected value is given by the system, and the DC power unit needs to control the actual DC bus voltage value to dynamically track the given value, and at the same time achieve current limiting.

[0055] ③ Power control mode: The current loop control mode shall be adopted. As shown in (c) of Figure 2 , the expected current value is obtained based on the expected DC bus power value, and the actual current value is dynamically tracked to the expected current value through PI control. At this time, the expected DC bus voltage side power value is given by the system, and the expected current value can be obtained according to this given value. The DC power unit controls the actual current value to dynamically track the given value.

[0056] 2) Forward and reverse, step-up and step-down operation of the DC power unit

[0057] After determining the control strategy of the DC power unit, the operating conditions of the main circuit part can be divided into 4 types: forward and reverse, step-up and step-down. To optimize the working performance of the DC / DC structure of the main circuit part, it is necessary to optimize the control quantity for different operating conditions to reduce the reflux power and improve the converter efficiency. Among them, the difference in the step-up and step-down conditions determines the duty ratio relationship of the inverter square waves of the primary and secondary side bridge arms of the converter; the difference in the forward and reverse conditions determines the phase relationship of the inverter square waves of the primary and secondary side bridge arms of the converter.

[0058] 3) The DC power unit changes from operation to stop

[0059] Suppose at a certain moment, the coordination control unit issues a command to stop the operation of a certain DC power unit, and this DC power unit needs to ensure a smooth switching of the operating state at a relatively fast response speed. To reduce the impact, the output power of the DC / DC structure in the main circuit part can be gradually reduced in the form of a ramp function, and the response speed can be adjusted by changing the slope. When the DC power unit completely stops, the pulses of the switching devices should be blocked to ensure the safety of the system. At this time, the DC power unit maintains communication with the control and management unit and waits for the next startup or the device to be removed from the solid-state power grid.

[0060] The AC power unit in this embodiment includes: a detection circuit part for detecting the three-phase grid line voltage and phase current, DC bus voltage and current, output voltage and current; a drive circuit part adopting a three-phase two-level converter structure or a CHB multi-level converter structure with a common DC bus; and a main control part for determining the control method of the drive circuit part according to the DC bus voltage control method issued by the coordination control unit.

[0061] Among them, the drive circuit part can choose the traditional three-phase two-level converter structure or be designed as a CHB multi-level converter structure with a common DC bus to realize directly connecting to the medium and high voltage distribution network without a power frequency transformer. According to the requirements of the actual operation scenario, flexible configuration and expansion can be carried out. The output interface of the AC power unit can be connected to the power grid or can be used as an AC source to supply power to local AC loads. The DC side of the AC power unit is connected to the DC bus, that is, the DC power unit and the AC power unit are connected through the DC bus. Under different DC bus voltage control methods, the control methods of the AC power unit are also different. For example, when the DC bus is controlled by the energy storage unit, the AC power unit can operate in grid-connected or off-grid constant voltage or constant power control. By controlling the grid-connected mode of the inverter, the flexible switching between grid-connected operation and off-grid operation of the solid-state microgrid can be realized. By controlling the amplitude and harmonic components of the inverter output voltage, the support for the power grid and the regulation of power quality can also be realized.

[0062] The AC power unit adopts vector control and can realize the four-quadrant operation mode of the system, that is, it can control the transmission direction and magnitude of active and reactive power respectively according to the requirements of the solid-state microgrid system. At the same time, according to the power quality of the grid voltage, by analyzing the grid voltage harmonics and injecting reverse harmonic voltage, the improvement of power quality can also be realized. The main control part of the AC power unit includes: a first control sub-unit for controlling the drive circuit part in grid-connected or off-grid constant voltage or constant power control when the DC bus is controlled by the energy storage unit; a second control sub-unit for controlling the drive circuit part to operate in the networking mode when the DC bus is connected to the grid through the control of the inverter. Among them, the control methods of the first control sub-unit and the second control sub-unit are as Figure 3 shown.

[0063] Figure 3 Among them, V pabc Inverter drive signal; U dc represents the DC bus voltage; i abc represents the three-phase output current of the converter, f pcc represents the grid frequency, θ pll represents the grid voltage rotation angle.

[0064] When the first control sub-unit controls the drive circuit part by constant voltage or constant power in grid-connected or off-grid mode, as Figure 3 shown in the phase-locked loop 1 in, its working process is as follows: Obtain the three-phase grid line voltage V pabc detected by the detection circuit part, and transform the three-phase grid line voltage V pabc into the port voltage V pαβ in the two-phase stationary coordinate system through coordinate transformation, and then transform the port voltage signal V pαβ in the two-phase stationary coordinate system into the voltage V pd and V pq in the two-phase rotating coordinate system, where the coordinate transformation angle signal is provided by the phase signal output by the phase-locked loop; input the q-axis voltage signal V pq into the PI controller to obtain the system real-time angular frequency deviation signal ω err , add the system real-time angular frequency deviation signal ω err and the rated angular frequency signal ω 0 to obtain the real-time angular frequency signal ω, and the real-time angular frequency signal ω passes through an integration link to obtain the phase angle signal reference θ pll of the whole system.

[0065] When the first control sub-unit controls the drive circuit part by constant voltage or constant power in grid-connected or off-grid mode, as Figure 3 shown in the coordinate transformation 2 in, according to the collected three-phase grid line voltage V pabc and phase current i abc , use the phase angle signal reference of the system to perform coordinate transformation to transform the three-phase grid line voltage V pabc into the voltage amplitude signal in the two-phase rotating coordinate system; transform the phase current i abc in the three-phase stationary coordinate system into the current signals I d and I q in the two-phase rotating coordinate system.

[0066] When the first control sub-unit controls the drive circuit part by constant voltage or constant power in grid-connected or off-grid mode, it also includes, as Figure 3As shown in the output active and reactive current calculation section 3, the system operates in the grid-connected operation mode under this section, and the management of the DC bus voltage is realized by the AC converter. Therefore, through the closed-loop control of the DC bus voltage, the output active current of the converter is calculated, and the DC bus voltage is adjusted by adjusting the output active power of the solid-state microgrid, as follows: According to the rated value U of the DC bus voltage dcref and the DC bus voltage U detected by the detection circuit part dc , the difference between the two is obtained to get the first deviation signal, and the first deviation signal is input into the DC bus voltage controller to obtain the d-axis current reference signal i dref ; According to the reactive power demand of the power grid system, a reactive power control link is introduced, and the difference between the reactive power reference value Q ref and the actual output value Q e is taken to obtain the second deviation signal, and the second deviation signal is input into the reactive power controller to obtain the q-axis current reference signal i qref .

[0067] The second control sub-unit is used to control the operation of the drive circuit part in the networking mode when the DC bus is connected to the grid through the inverter. In the networking mode, as Figure 3 shown, according to the rated value U of the DC bus voltage dcref and the DC bus voltage U detected by the detection circuit part dc , the difference between the two is obtained to get the first deviation signal, and the first deviation signal is input into the DC bus voltage controller 4; the grid voltage frequency deviation is input into the synchronous generator speed governor 5; the output power is adjusted through the DC bus voltage controller 4 and the synchronous generator speed governor 5, so as to realize the primary frequency modulation ability of the solid-state microgrid. Then, based on the output of the DC bus voltage controller and the output of the synchronous generator speed governor, the active power set value P ref is obtained, and the deviation between the active power set value P ref and the actual output value P e is input into the synchronous machine rotor swing equation 6 to obtain the power synchronizer angular frequency deviation signal Δω. The power synchronizer angular frequency deviation signal Δω and the rated angular frequency signal ω 0 are added to obtain the system real-time angular frequency signal ω, and finally the phase angle signal reference θ vsg is obtained through the integrator; the deviation between the real-time voltage amplitude U pf measured at the grid connection point and the rated value U of the grid connection point voltage N is input into the droop controller 7 to generate a reactive power regulation deviation signal, and a power synchronous output voltage reference value is generated through the reactive power loop 8; based on the power synchronous output voltage reference value, coordinate transformation 9 is performed using the phase angle signal reference to obtain the output voltage reference values V dref and V qref, and input the closed-loop of the output voltage synchronized with the input power to obtain the reference value of the d-axis current \(i_{d}^{*}\) dref and the reference value of the q-axis current \(i_{q}^{*}\) qref ; According to the reference value of the d-axis current \(i_{d}^{*}\) dref , the reference value of the q-axis current \(i_{q}^{*}\) qref , respectively compare with the actual d-axis current \(i_{d}\) d and the q-axis current \(i_{q}\) q to obtain the d-axis error signal and the q-axis error signal. The d-axis error signal and the q-axis error signal are respectively subjected to closed-loop control by a PI controller 10 to obtain the adjusted voltage on the output filter inductor. By superimposing with the grid connection point feed-forward voltage, the output modulation voltage is generated. According to the phase information, inverse coordinate transformation is performed to obtain the modulation voltage in the two-phase stationary coordinate system; the modulation voltage in the two-phase stationary coordinate system is input into the SVPWM module 11 for processing to obtain the drive signal of the drive circuit part.

[0068] It is not difficult to find that in order to adapt to the access of various energy sources, loads and energy storage devices, the present invention provides great flexibility and scalability through the modularized AC / DC unit and diverse interfaces, efficiently integrates different types of energy and loads, and enhances the interface adaptability. In order to ensure the stable operation and flexible control of the solid-state microgrid system, the present invention adopts an overall control method of hybrid cooperative control. Through the interaction between the main controller and the state information and operating conditions of each unit, the port devices are intelligently identified and the operating mode output power of each sub-unit is adjusted, etc., to adapt to different application scenarios. At the same time, intelligent microgrid control algorithms such as fault protection, grid connection / disconnection control, and power quality management are embedded to realize the cross-layer integration of the system, thus having the advantages of high adaptability and high reliability.

[0069] This embodiment also relates to the control method of the above-mentioned solid-state microgrid system. The solid-state microgrid in this embodiment adopts a system structure with highly integrated hardware circuits and control systems to achieve the purpose of improving the converter conversion, optimizing the architecture, efficiency and economy of the microgrid system, minimizing the transmission and distribution links, thereby reducing the fault risk, quickly responding to the fluctuations of the power supply and load, and ensuring the stability of the system. Figure 4 It is the adaptive cooperative control integration diagram of the solid-state microgrid system control method. Through the integrated system layer control, flexible and unified control of each power unit in the solid-state microgrid can be realized, so as to achieve the purpose of adaptively and cooperatively controlling each power unit according to the actual operating conditions of the system.

[0070] Among them, device-level control refers to achieving control objectives for the DC power units and AC power units (such as bidirectional DC / AC converters, AC-DC load interface converters, DC load interface converters, distributed power source interface converters, and energy storage device interface converters, etc.) at the physical layer of the solid-state microgrid based on control information. The DC power unit performs intelligent identification according to the interface. When the DC port of the DC power unit is not connected, the circuit remains in a locked state. At this time, all switching devices of the DC / DC converter are blocked, and there is no energy transfer. After an external device is connected to the bus interface, the control and management unit identifies the connected device and performs corresponding identification, management, and control according to the port type. The main task of device-level control is to maintain the stability of the DC bus voltage, achieve power balance within the system, and ensure the safe and reliable operation of the solid-state microgrid. As Figure 4 shown, for different interface converters and different control objectives, its device-level control strategies are also different, mainly including: DC bus voltage control, AC-DC interconnection power control, AC-DC load voltage control, maximum power tracking, voltage-power droop control, and constant power / current charge and discharge control, etc.

[0071] As Figure 4 shown, the main purpose of system-level control is to provide an interface for the upper-level power grid, achieve centralized management of the micro-sources and loads accessed by the solid-state microgrid, and improve the operation efficiency and reliability of the solid-state microgrid. Energy management and optimal operation are the main control objectives of system-level control, and functional modules such as DC bus voltage regulation and smooth switching between multiple operation modes are important components to achieve this control objective. According to the state of the input power fluctuation of the DC power unit, etc., combined with the charge and discharge state of the energy storage, analyze the change characteristics of the DC voltage under different working conditions, coordinate the power transmission capacity between the AC and DC powers based on the DC voltage information, and combine the actual requirements of multiple operation modes such as grid connection, off-grid, energy storage battery charge / discharge, power energy dispatching, peak shaving and valley filling, etc., to smoothly switch the operation mode of the solid-state microgrid system. Achieving reasonable distribution of the output power of each power generation unit is one of the key objectives in the system-level operation control of the solid-state microgrid. Under grid-connected operation, according to the system output power and the state of the DC bus voltage, control the solid-state microgrid to adaptively adjust the interconnection transmission power with the upper-level power grid. When the solid-state microgrid operates independently, according to the state of charge of the energy storage unit in the system and the power demand, automatically manage the distributed power sources, energy storage, and loads, and coordinate the power and energy distribution of the power generation units to ensure that the main control unit (such as the energy storage device) in the microgrid can control the stability of the bus voltage.

[0072] The coordination strategy of this embodiment starts from the perspective of the system level. According to the actual operating conditions of the system, it adaptively and coordinately controls the operating modes of each functional unit of the solid-state microgrid, achieving the goal of high adaptability operation of the system. Intelligent microgrid control algorithms such as fault protection, grid connection and disconnection control, and power management are embedded at the system layer. By real-time monitoring the status signals such as voltage and current at each port, it coordinates the operating states of each power unit, realizes power flow control and energy management, effectively reduces the adverse effects brought by large-scale utilization of renewable energy to the safe and stable operation of the distribution network, and realizes the high efficiency, high adaptability and high reliability of the entire solid-state microgrid system, as well as the cross-level functional integration and fusion.

Claims

1. A solid-state microgrid system, characterized in that: include: A DC bus is connected to a DC bus port; the DC bus port is used to connect a DC load; The DC power unit adopts a modular design, the input side is connected to the DC port, and the output side is connected to the DC bus; the DC port is used to connect the distributed energy storage device; the DC power unit includes: The sampling circuit part is used to sample the voltage and current of the DC port and the voltage and current of the DC bus; The main circuit adopts a DC / DC structure that can realize bidirectional energy flow and has high-frequency isolation; The control circuit part is used to identify the inserted device on the DC port side, transmit the identification result to the coordination control unit, and control the operation state of the main circuit part according to the control strategy of the DC power unit issued by the coordination control unit; The AC power unit adopts a modular design, the DC side is connected to the DC bus, and the AC side is connected to the AC port; the AC port is used to connect to the AC grid; the AC power unit includes: The detection circuit part is used to detect the three-phase grid line voltage and phase current, DC bus voltage and current, output voltage and current; The driving circuit part adopts a three-phase two-level converter structure or a CHB multi-level converter structure with a common DC bus; the main control part is used to determine the control method of the driving circuit part according to the DC bus voltage control method issued by the coordination control unit; the main control part includes: A first control subunit, used to control the driving circuit part by adopting a grid-connected or off-grid constant voltage or constant power when the DC bus is controlled by the energy storage unit; A second control subunit is used to control the driving circuit part to operate in a networking mode when the DC bus is connected to the grid by controlling the inverter; When the first control subunit uses a grid-connected or off-grid constant voltage or constant power to control the driving circuit part, the three-phase grid line voltage V detected by the detection circuit part is obtained. pabc , through coordinate transformation, the three-phase grid line voltage V pabc Transformed into the voltage V in the two-phase rotating coordinate system pd and V pq , the q-axis voltage signal V pq Input the PI controller to get the system real-time angular frequency deviation signal ω err , the system real-time angular frequency deviation signal ω err The real-time angular frequency signal ω is added to the rated angular frequency signal ω0, and the real-time angular frequency signal ω is integrated to obtain the phase angle signal reference θ of the whole system. pll ; When the first control subunit adopts the constant voltage or constant power control of the driving circuit part in grid connection or off-grid connection, the three-phase grid line voltage V pabc and phase current i abc , use the system's phase angle signal reference to perform coordinate transformation to convert the three-phase grid line voltage V pabc The voltage amplitude signal is transformed into the two-phase rotating coordinate system; the phase current i in the three-phase stationary coordinate system is transformed into the voltage amplitude signal in the two-phase rotating coordinate system; abc The current signal I transformed into the two-phase rotating coordinate system d and I q ; When the first control subunit adopts the constant voltage or constant power control of the driving circuit part in grid connection or off-grid connection, according to the rated value of the DC bus voltage U dcref The DC bus voltage U detected by the detection circuit dc The first deviation signal is input into the DC bus voltage controller to obtain the d-axis current reference signal i dref According to the reactive power demand of the power grid system, the reactive power control link is introduced to set the reactive power reference value Q ref and the actual output value Q e The second deviation signal is input into the reactive power controller to obtain the q-axis current reference signal i qref ; A coordination control unit is respectively connected to the DC power unit and the AC power unit, and is used to realize at least one of energy access, conversion, distribution, control and management; the coordination control unit is also used to determine the control strategy of the DC power unit according to the identification result of the inserted device on the DC port side.

2. The solid-state microgrid system according to claim 1, characterized in that: The control strategy of the DC power unit includes a DC port voltage control mode, a DC bus voltage control mode and a power control mode; in the DC port voltage control mode, the DC bus voltage is not controlled, the DC port voltage is controlled, and the direction and magnitude of power flow are determined by the load; in the DC bus voltage control mode, the DC port voltage is not controlled, the DC bus voltage is controlled, and the direction and magnitude of power flow are determined by the load; in the power control mode, neither the DC bus voltage nor the DC port voltage is controlled, and only the magnitude and direction of power flow are controlled.

3. The solid-state microgrid system according to claim 2, characterized in that: When the control strategy of the DC power unit received is the DC port voltage control mode, the control circuit part obtains a DC port current reference value through closed-loop control according to the expected voltage value of the DC port and the voltage of the DC port obtained by the sampling circuit part, and then obtains a preliminary DC port current control value through closed-loop control according to the DC port current reference value and the current of the DC port obtained by the sampling circuit part, and then performs current limiting on the preliminary DC port current control value to obtain a final DC port current control value; optimizes the control amount according to the current working condition of the main circuit part; When the control strategy of the DC power unit received is the DC bus voltage control mode, the control circuit part obtains a DC bus current reference value through closed-loop control according to the DC bus voltage expected value and the DC bus voltage obtained by the sampling circuit part, and then obtains a bus voltage preliminary current control value through closed-loop control according to the DC bus current reference value and the DC bus current obtained by the sampling circuit part, and then performs current limiting on the preliminary bus voltage current control value to obtain a bus voltage final current control value; optimize the control amount according to the current working condition of the main circuit part; When the control strategy of the DC power unit received is the power control mode, the control circuit part obtains the expected current value according to the expected value of the DC bus power, and dynamically tracks the actual current value to the expected current value through closed-loop control; Optimize the control quantity according to the current working conditions of the main circuit.

4. The solid-state microgrid system according to claim 1, characterized in that: When the second control subunit controls the drive circuit part to operate in the networking mode, according to the DC bus voltage rated value U dcref The DC bus voltage U detected by the detection circuit dc , the difference between the two is obtained to obtain a first deviation signal, and the first deviation signal is input into the DC bus voltage controller; the grid voltage frequency deviation is input into the synchronous generator speed regulator; based on the output of the DC bus voltage controller and the output of the synchronous generator speed regulator, the active power setting value P is obtained. ref , set the active power value P ref and the actual output value P e The deviation is input into the synchronous machine rotor swing equation to obtain the power synchronizer angular frequency deviation signal Δω. The power synchronizer angular frequency deviation signal Δω and the rated angular frequency signal ω0 are added to obtain the system real-time angular frequency signal ω. The phase angle signal reference θ is finally obtained through the integrator. vsg ; The real-time voltage amplitude U of the grid connection point measured by the grid connection point pf The grid voltage rating U N The deviation input droop controller generates a reactive power regulation deviation signal, and generates a power synchronous output voltage reference value through a reactive power loop; based on the power synchronous output voltage reference value, a phase angle signal reference is used to perform coordinate conversion to obtain an output voltage reference value V dref and V qref , and input the power synchronous output voltage closed loop to obtain the d-axis current reference value i dref and q-axis current reference value i qref ; According to the d-axis current reference value i dref , q-axis current reference value i qref and the actual d-axis current i d and q-axis current i q Comparison is performed to obtain a d-axis error signal and a q-axis error signal, and the d-axis error signal and the q-axis error signal are respectively closed-loop controlled by a PI controller to obtain an adjustment voltage on the output filter inductor, which is superimposed with a grid-connected point feedforward voltage to generate an output modulation voltage, and an inverse coordinate transformation is performed according to phase information to obtain a modulation voltage in a two-phase stationary coordinate system; the modulation voltage in the two-phase stationary coordinate system is input into a space vector pulse width modulation module for processing to obtain a drive signal of the drive circuit part.

5. A control method for a solid-state microgrid system as claimed in any one of claims 1 to 4, characterized in that: It includes device-level control, and the device-level control refers to completing the control target of the AC power unit and the DC power unit of the physical layer of the solid-state microgrid based on control information.

6. The control method of the solid-state microgrid system according to claim 5, characterized in that: This includes system-level control, the purpose of which is to provide an interface for the upper power grid.

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