A multi-bus three-phase mixed network inverter integrated system

Abstract

The application provides a multi-bus three-phase mixed-grid inverter integrated system, comprising a photovoltaic input bus unit, an energy storage bus unit, a first common DC bus unit, a second DC load bus unit, a three-phase mixed-grid inverter unit, a three-phase AC load bus unit, a three-phase power grid bus unit, a bus connection switching unit, a sampling protection unit and a main control unit; the photovoltaic input bus unit is connected to the first common DC bus unit through a photovoltaic DC / DC conversion module; the energy storage bus unit is connected to the first common DC bus unit through a bidirectional DC / DC conversion module; the second DC load bus unit is connected to the first common DC bus unit through a DC connection switch; and the DC side of the three-phase mixed-grid inverter unit is connected to the first common DC bus unit. The application solves the problems of low integration, large bus fluctuation, obvious switching impact and insufficient fault isolation capacity of the existing system.

Description

Technical Field

[0001] This invention relates to the field of power supply systems, and more particularly to a multi-bus three-phase hybrid grid inverter integrated system. Background Technology

[0002] With the widespread application of photovoltaic power generation, energy storage systems, DC loads, and three-phase AC loads in industrial and commercial power supply, off-grid power supply, and microgrid scenarios, traditional single inverter or single bus power supply structures are no longer sufficient to meet the needs of multi-energy and multi-load coordinated operation. Existing photovoltaic inverter equipment typically focuses on photovoltaic maximum power point tracking and AC output, while energy storage converter equipment focuses on battery charge and discharge management. DC load power supply and three-phase AC load power supply often require external distribution cabinets, bypass cabinets, or combinations of multiple independent converters. Such solutions involve a large number of devices, complex wiring, and dispersed control links, which is not conducive to system integration and on-site installation and maintenance.

[0003] In AC / DC hybrid power supply systems, fluctuations in photovoltaic output, changes in energy storage charging and discharging, DC load switching, and sudden changes in three-phase AC loads can all cause DC bus voltage fluctuations. When the grid experiences anomalies or grid connection / disconnection switching, it can also easily cause AC output voltage drops, frequency disturbances, phase jumps, or even short-term load power outages. Existing technologies mostly employ single DC bus voltage regulation or single inverter control methods, which are difficult to simultaneously meet the multiple operational requirements such as photovoltaic input, energy storage support, DC load power supply, three-phase AC power supply, grid parallel operation, and fault isolation.

[0004] Meanwhile, existing on-grid / off-grid switching methods typically rely on external control devices to complete synchronization and switching decisions, and the equipment-level inverter itself lacks multi-bus coordinated control capabilities. When a fault occurs on a certain bus or a certain load, it is often necessary to shut down the entire system for protection, which forces non-faulty loads to lose power as well, reducing the reliability of the system power supply.

[0005] Therefore, it is necessary to provide a new multi-bus three-phase hybrid grid inverter integrated system to solve the above-mentioned technical problems. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a multi-bus three-phase mixed-network inverter integrated system, which solves the problems of low integration, large bus fluctuations, significant switching impacts, and insufficient fault isolation capabilities in existing systems.

[0007] The multi-bus three-phase hybrid grid inverter integrated system provided by this invention includes: The system includes a photovoltaic input bus unit, an energy storage bus unit, a first common DC bus unit, a second DC load bus unit, a three-phase mixed-network inverter unit, a three-phase AC load bus unit, a three-phase power grid bus unit, a bus tie switching unit, a sampling protection unit, and a main control unit. The photovoltaic input bus unit is connected to the first common DC bus unit through a photovoltaic DC / DC conversion module; The energy storage bus unit is connected to the first common DC bus unit via a bidirectional DC / DC converter module; The second DC load bus unit is connected to the first common DC bus unit via a DC interconnection switch; The DC side of the three-phase mixed-grid inverter unit is connected to the first common DC bus unit, and the AC side of the three-phase mixed-grid inverter unit is connected to the three-phase AC load bus unit through load switches and to the three-phase power grid bus unit through grid connection switches. The bus tie switching unit includes the DC tie switch, the load switch, and the grid connection switch; The sampling protection unit is connected to the photovoltaic input bus unit, the energy storage bus unit, the first common DC bus unit, the second DC load bus unit, the three-phase AC load bus unit, and the three-phase power grid bus unit, respectively, and is used to collect the voltage, current, power, and switch status of each bus. The main control unit is connected to the photovoltaic DC / DC conversion module, the bidirectional DC / DC conversion module, the three-phase mixed-grid inverter unit, the bus tie switching unit, and the sampling protection unit, respectively. It is used to control the working state of the photovoltaic DC / DC conversion module, the bidirectional DC / DC conversion module, the three-phase mixed-grid inverter unit, and the bus tie switching unit according to the data collected by the sampling protection unit, so that the multi-bus three-phase mixed-grid inverter integrated system can switch between grid-connected power supply, off-grid power supply, rectification charging, bypass power supply, and fault isolation states.

[0008] Preferably, the photovoltaic input bus unit includes at least one photovoltaic input port, a photovoltaic voltage sampling circuit, a photovoltaic current sampling circuit, a reverse connection protection circuit, and an input protection switch; The photovoltaic DC / DC conversion module is controlled by the main control unit and has a maximum power point tracking working state, a constant voltage and current limiting working state, a power limiting working state, and a fault exit working state. When the voltage of the first common DC bus unit is within the normal adjustment range, the photovoltaic DC / DC conversion module operates in maximum power point tracking mode. When the voltage of the first common DC bus unit is higher than the preset power limit threshold, the main control unit controls the photovoltaic DC / DC conversion module to reduce the output power. When the photovoltaic input bus unit experiences an overvoltage, overcurrent, or reverse connection fault, the main control unit controls the input protection switch to open and causes the photovoltaic DC / DC converter module to enter a fault exit working state.

[0009] Preferably, the energy storage bus unit includes an energy storage battery interface, a battery voltage sampling circuit, a battery current sampling circuit, a battery temperature sampling circuit, and an energy storage protection switch; The bidirectional DC / DC converter module has charging operation mode, discharging operation mode, float charging operation mode and standby operation mode. When the voltage of the first common DC bus unit is lower than the preset discharge threshold, the main control unit controls the bidirectional DC / DC converter module to enter the discharge working state in order to compensate the power of the first common DC bus unit. When the voltage of the first common DC bus unit is higher than the preset charging threshold and the state of charge of the energy storage bus unit is lower than the preset upper limit, the main control unit controls the bidirectional DC / DC converter module to enter the charging working state. When the state of charge of the energy storage bus unit is higher than the preset upper limit, the main control unit prioritizes controlling the photovoltaic DC / DC conversion module to enter the power-limited working state.

[0010] Preferably, the first common DC bus unit includes a DC bus capacitor, a bus pre-charge circuit, a bus voltage sampling circuit, a bus current sampling circuit, and DC protection devices; The second DC load bus unit includes a DC load output port, a DC load voltage sampling circuit, and a DC load current sampling circuit; Before closing the DC interconnection switch, the main control unit first controls the bus pre-charging circuit to pre-charge the second DC load bus unit, and controls the DC interconnection switch to close after the voltage difference between the first common DC bus unit and the second DC load bus unit is less than a preset voltage difference threshold. Before disconnecting the DC-DC interconnection switch, the main control unit first reduces the current flowing through the DC-DC interconnection switch, and then controls the DC-DC interconnection switch to disconnect after the current is less than a preset disconnection threshold.

[0011] Preferably, the three-phase mixed-grid inverter unit includes a three-phase power bridge, an AC filter inductor, an AC filter capacitor, a three-phase AC voltage sampling circuit, a three-phase AC current sampling circuit, and a drive protection circuit. The three-phase grid-connected inverter unit operates in grid-connected current source control state when the three-phase grid bus unit is normal, and is used to output or absorb power to the three-phase grid bus unit according to the active power command and reactive power command given by the main control unit. The three-phase mixed-grid inverter unit operates in off-grid voltage source control state when the three-phase grid bus unit is abnormal, and is used to provide three-phase AC voltage to the three-phase AC load bus unit. In the rectified charging state, the three-phase hybrid inverter unit absorbs AC power from the three-phase power grid bus unit and charges the energy storage bus unit through the first common DC bus unit.

[0012] Preferably, the main control unit includes a grid-connected / off-grid switching control module; When switching from off-grid to on-grid, the on-grid switching control module first detects the voltage amplitude difference, frequency difference, and phase difference between the three-phase AC load bus unit and the three-phase power grid bus unit, and controls the grid connection switch to close after the voltage amplitude difference, frequency difference, and phase difference all meet the preset grid connection conditions. When switching from grid connection to off-grid, the grid-connected switching control module first controls the three-phase mixed-grid inverter unit to reduce the switching power or switching current at the grid connection switch, and then controls the grid connection switch to disconnect after the switching power or switching current is lower than the preset switching threshold. After the grid-connected switch is disconnected, the three-phase mixed-grid inverter unit retains the output voltage amplitude, frequency and phase before disconnection as the initial control variables for the off-grid voltage source control state.

[0013] Preferably, the main control unit includes a three-phase imbalance compensation module; The three-phase imbalance compensation module extracts the positive sequence component and negative sequence component of the three-phase AC load bus unit based on the data collected by the three-phase AC voltage sampling circuit and the three-phase AC current sampling circuit. When the voltage imbalance of the three-phase AC load bus unit is higher than the preset imbalance threshold, the three-phase imbalance compensation module generates a negative sequence compensation current command and superimposes the negative sequence compensation current command into the current control loop of the three-phase mixed-network inverter unit to reduce the voltage imbalance of the three-phase AC load bus unit. When the three-phase AC load bus unit is a three-phase four-wire output structure, the three-phase unbalance compensation module also generates a zero-sequence compensation command based on the neutral current to suppress the neutral current.

[0014] Preferably, the main control unit includes a fault isolation control module; The fault isolation control module identifies photovoltaic input faults, energy storage faults, first common DC bus faults, second DC load bus faults, three-phase AC output faults, and three-phase power grid faults based on the data collected by the sampling protection unit. When a photovoltaic input fault is detected, the fault isolation control module controls the photovoltaic input bus unit to exit operation; When an energy storage fault is detected, the fault isolation control module controls the energy storage protection switch to disconnect. When a fault is detected in the second DC load bus, the fault isolation control module controls the DC interconnection switch to disconnect. When a three-phase power grid fault is detected, the fault isolation control module controls the grid-connected switch to open and controls the three-phase mixed-grid inverter unit to enter the off-grid voltage source control state. When a three-phase AC output fault is detected, the fault isolation control module controls the load switch or the corresponding branch switch to disconnect according to the load priority, so as to keep the non-faulty busbar running.

[0015] The beneficial effects of this invention are: 1. This invention integrates the photovoltaic input bus, energy storage bus, first common DC bus, second DC load bus, three-phase AC load bus, and three-phase power grid bus into the same inverter integrated system, and achieves connection through corresponding conversion modules and tie switches. This reduces the dispersed configuration of external converters, switching cabinets, and power distribution equipment, and helps to reduce the complexity of system wiring and the difficulty of on-site installation and maintenance.

[0016] 2. This invention uses the first common DC bus as the energy collection node between photovoltaic, energy storage, DC load and three-phase mixed grid inverter unit. The main control unit coordinates the working status of photovoltaic DC / DC conversion module, bidirectional DC / DC conversion module and three-phase mixed grid inverter unit, so that multiple power modules can participate in bus voltage stabilization and power balance, thereby reducing DC bus voltage fluctuations caused by photovoltaic output fluctuations, load changes and energy storage charging and discharging changes.

[0017] 3. This invention provides a second DC load bus, which is connected to the first common DC bus via a DC tie switch. The main control unit performs pre-charging and differential voltage judgment before the tie switch is closed, and performs current limiting judgment before the tie switch is opened, which can reduce the surge current generated when the DC load is connected or disconnected, and reduce the impact on the main DC bus.

[0018] 4. The three-phase mixed-grid inverter unit of the present invention can switch between grid-connected current source control, off-grid voltage source control and rectifier charging state according to the three-phase grid bus status; and when switching from off-grid to grid-connected, voltage, frequency and phase synchronization are performed first, and when switching from grid-connected to off-grid, the switching power or switching current is reduced first and then the grid-connected switch is disconnected, thereby reducing voltage surges and power surges during the grid-connected to off-grid switching process and improving the continuity of power supply to three-phase AC loads.

[0019] 5. This invention uses a three-phase unbalanced compensation module and a fault isolation control module to detect and process the unbalanced state of the three-phase AC load bus and the fault state of each branch. When an unbalanced load or local fault occurs, the system can compensate or disconnect the corresponding faulty branch, maintaining the operation of the non-faulty bus and important loads, thereby improving the power supply quality and operational reliability of the system. Attached Figure Description

[0020] Figure 1 A schematic diagram of the multi-bus three-phase hybrid grid inverter integrated system provided by the present invention; Figure 2 This is a schematic diagram of the control structure of the main control unit provided by the present invention; Figure 3 The following is a flowchart of the grid-connected / off-grid switching control provided by the present invention; Figure 4 This is a schematic diagram of multi-bus coordinated control and fault isolation provided by the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Please refer to the following: Figure 1 , Figure 2 , Figure 3 as well as Figure 4 ,in Figure 1 A schematic diagram of the multi-bus three-phase hybrid grid inverter integrated system provided by the present invention; Figure 2 This is a schematic diagram of the control structure of the main control unit provided by the present invention; Figure 3 The following is a flowchart of the grid-connected / off-grid switching control provided by the present invention; Figure 4 This is a schematic diagram of multi-bus coordinated control and fault isolation provided by the present invention.

[0023] In the specific implementation process, such as Figures 1-4 As shown, this embodiment provides a multi-bus three-phase hybrid grid inverter integrated system. This system is suitable for power supply scenarios where photovoltaic power generation, energy storage batteries, DC loads, three-phase AC loads, and three-phase grids are simultaneously connected. It is particularly suitable for industrial and commercial energy storage systems, AC / DC hybrid power supply systems, off-grid power supply systems, communication base station power supply systems, emergency power supply systems, and small AC / DC hybrid microgrid systems.

[0024] The multi-bus three-phase mixed grid inverter integrated system of this embodiment includes a photovoltaic input bus unit, an energy storage bus unit, a first common DC bus unit, a second DC load bus unit, a three-phase mixed grid inverter unit, a three-phase AC load bus unit, a three-phase grid bus unit, a bus tie switching unit, a sampling protection unit, and a main control unit.

[0025] The photovoltaic input bus unit is connected to the first common DC bus unit via a photovoltaic DC / DC converter module. The energy storage bus unit is connected to the first common DC bus unit via a bidirectional DC / DC converter module. The second DC load bus unit is connected to the first common DC bus unit via a DC tie switch. The DC side of the three-phase mixed-grid inverter unit is connected to the first common DC bus unit, and the AC side is connected to the three-phase AC load bus units via load switches, and to the three-phase grid bus unit via a grid-connected switch.

[0026] The first common DC bus unit serves as the system's main energy collection bus, receiving electrical energy from the photovoltaic input bus unit, the energy storage bus unit (either output or absorbed), and the energy exchanged between the three-phase hybrid inverter unit and the AC side. The second DC load bus unit acts as an independent DC power supply bus, connecting DC lighting equipment, communication equipment, DC charging equipment, or other DC loads. The three-phase AC load bus unit connects three-phase AC loads, and the three-phase grid bus unit connects to an external three-phase power grid.

[0027] The main control unit is connected to the photovoltaic DC / DC conversion module, the bidirectional DC / DC conversion module, the three-phase mixed grid inverter unit, the bus tie switching unit, and the sampling protection unit, respectively. It is used to coordinate and control each power module and each bus switch according to the data collected by the sampling protection unit, so that the system can switch between grid-connected power supply, off-grid power supply, rectification charging, bypass power supply, black start, and fault isolation.

[0028] In a preferred embodiment, the rated voltage of the first common DC bus unit is 700V, the rated output voltage of the three-phase AC load bus unit is AC380V, and the rated frequency is 50Hz. In other embodiments, the rated voltage of the first common DC bus unit can also be set to 400V, 750V, 800V, or other applicable voltage levels, and the three-phase AC output voltage can also be set to AC220V, AC380V, or AC400V depending on the application scenario.

[0029] The photovoltaic input bus unit includes at least one photovoltaic input port, a photovoltaic voltage sampling circuit, a photovoltaic current sampling circuit, a reverse connection protection circuit, an input protection switch, and a photovoltaic DC / DC conversion module.

[0030] The photovoltaic input port is used to connect photovoltaic module strings. A photovoltaic voltage sampling circuit is used to collect the photovoltaic input voltage, and a photovoltaic current sampling circuit is used to collect the photovoltaic input current. The main control unit calculates the photovoltaic input power based on the photovoltaic input voltage and photovoltaic input current, and controls the duty cycle of the photovoltaic DC / DC converter module according to changes in the photovoltaic input power.

[0031] Photovoltaic input power is calculated using the following formula:

[0032] in, For photovoltaic input power, Photovoltaic input voltage, This is the input current for photovoltaics.

[0033] In this embodiment, the photovoltaic DC / DC converter module adopts a Boost topology, with its input connected to the photovoltaic input bus unit and its output connected to the first common DC bus unit. The photovoltaic DC / DC converter module can operate in maximum power point tracking mode, constant voltage and current limiting mode, power limiting mode, and fault exit mode.

[0034] When the voltage of the first common DC bus unit is within the normal range, the main control unit controls the photovoltaic DC / DC converter module to operate in maximum power point tracking (MPPT) mode. MPPT can be achieved using the perturbation-observation method, the incremental conductance method, or the constant voltage method. This embodiment preferably uses the perturbation-observation method.

[0035] When the main control unit detects that the voltage of the first common DC bus is higher than the preset power limit threshold, the main control unit reduces the output power of the photovoltaic DC / DC converter module, causing the photovoltaic input unit to switch from maximum power point tracking state to power limit state. This control method can avoid overvoltage of the DC bus caused by the photovoltaic continuously injecting power into the first common DC bus when the energy storage battery is fully charged or the AC load is small.

[0036] When overvoltage, overcurrent, reverse connection, or insulation abnormality occurs at the photovoltaic input terminal, the main control unit controls the input protection switch to open and puts the photovoltaic DC / DC conversion module into fault exit state.

[0037] The energy storage bus unit includes an energy storage battery interface, a battery voltage sampling circuit, a battery current sampling circuit, a battery temperature sampling circuit, an energy storage protection switch, and a bidirectional DC / DC converter module.

[0038] The energy storage battery interface is used to connect lithium battery packs, lead-acid battery packs, sodium-ion battery packs, supercapacitors, or hybrid energy storage devices. The battery voltage sampling circuit is used to collect the terminal voltage of the energy storage battery, the battery current sampling circuit is used to collect the battery current, and the battery temperature sampling circuit is used to collect the battery temperature.

[0039] One end of the bidirectional DC / DC converter module is connected to the energy storage bus unit, and the other end is connected to the first common DC bus unit. The bidirectional DC / DC converter module has charging operation mode, discharging operation mode, float charging operation mode, and standby operation mode.

[0040] When the voltage of the first common DC bus is lower than the preset discharge threshold, the main control unit controls the bidirectional DC / DC converter module to enter the discharge working state, and the energy storage battery compensates the power to the first common DC bus unit.

[0041] When the voltage of the first common DC bus is higher than the preset charging threshold and the state of charge of the energy storage battery is lower than the preset upper limit, the main control unit controls the bidirectional DC / DC converter module to enter the charging working state, and charges the energy storage battery from the first common DC bus.

[0042] When the state of charge of the energy storage battery is higher than the preset upper limit, the main control unit prioritizes controlling the photovoltaic DC / DC conversion module to enter the power limiting state to avoid the energy storage being unable to continue absorbing energy, which would lead to overvoltage on the first common DC bus.

[0043] In this embodiment, the energy storage power reference value is determined jointly based on the DC bus voltage deviation, load power change, and energy storage state of charge deviation, and the calculation relationship is as follows:

[0044] in, This is a reference value for energy storage capacity. The reference voltage for the first common DC bus. This is the actual voltage of the first common DC bus. This represents the change in load power. For energy storage target state of charge, For energy storage, the current state of charge, , , This is the corresponding adjustment coefficient.

[0045] when When the value is greater than zero, the bidirectional DC / DC converter module performs discharge control; when When the value is less than zero, the bidirectional DC / DC converter module performs charging control; when... When the voltage is close to zero and within the set dead zone, the bidirectional DC / DC converter module enters a float charge or standby state.

[0046] The first common DC bus unit includes a DC bus capacitor, a bus pre-charge circuit, a bus voltage sampling circuit, a bus current sampling circuit, and DC protection devices. The second DC load bus unit includes a DC load output port, a DC load voltage sampling circuit, and a DC load current sampling circuit.

[0047] The first common DC bus unit serves as the common energy exchange node for the photovoltaic input, energy storage unit, and three-phase grid-connected inverter unit. The second DC load bus unit is connected to the first common DC bus unit via a DC tie switch. To prevent the second DC load bus unit from impacting the first common DC bus unit when it is switched on, this embodiment includes a bus pre-charging process. Before closing the DC tie switch, the main control unit controls the bus pre-charging circuit to pre-charge the second DC load bus unit, causing its voltage to gradually increase.

[0048] When the voltage difference between the first common DC bus voltage and the second DC load bus voltage is less than a preset voltage difference threshold, the main control unit controls the DC interconnection switch to close.

[0049] The closing condition for the DC interconnection switch is:

[0050] in, The voltage of the first common DC bus. This is the voltage of the second DC load bus. The differential pressure threshold that allows closure.

[0051] When it is necessary to disconnect the second DC load bus unit, the main control unit first reduces the current flowing through the DC tie switch, and then controls the DC tie switch to disconnect after the current is less than the preset disconnection threshold.

[0052] The conditions for disconnecting the DC tie switch are:

[0053] in, The current flowing through the DC tie switch, The current threshold that allows disconnection.

[0054] The pre-charging and current-limiting disconnection control described above can reduce inrush current and switching impact during DC bus interconnection.

[0055] The three-phase mixed-grid inverter unit includes a three-phase power bridge, an AC filter inductor, an AC filter capacitor, a three-phase AC voltage sampling circuit, a three-phase AC current sampling circuit, and a drive protection circuit.

[0056] The three-phase power bridge can be constructed using IGBTs, MOSFETs, SiCMOSFETs, or GaN power devices. The DC side of the three-phase power bridge is connected to the first common DC bus unit, and the AC side is connected to the three-phase AC load bus unit and the three-phase power grid bus unit after passing through AC filter inductors and AC filter capacitors.

[0057] The three-phase mixed-grid inverter unit has grid-connected current source control state, off-grid voltage source control state, rectification and charging state, and bypass coordination state.

[0058] Under grid-connected current source control, the three-phase mixed-grid inverter unit outputs or absorbs power to the three-phase grid bus unit according to the active power command and reactive power command issued by the main control unit.

[0059] Under off-grid voltage source control, the three-phase mixed-grid inverter unit independently establishes three-phase AC voltage to supply power to the three-phase AC load bus unit.

[0060] In the rectified charging state, the three-phase hybrid inverter unit absorbs AC power from the three-phase grid bus unit and charges the energy storage bus unit through the first common DC bus unit.

[0061] In bypass coordination mode, the main control unit controls the bypass branch or grid connection switch to enable the three-phase grid bus unit to directly supply power to the three-phase AC load bus unit. At the same time, the three-phase mixed grid inverter unit enters standby, charging or power compensation mode as needed.

[0062] When the three-phase power grid bus unit is normal, the main control unit detects the three-phase power grid voltage, power grid frequency, power grid phase sequence, and power grid phase. When the power grid voltage amplitude, frequency, and phase sequence all meet the preset conditions, the main control unit controls the three-phase hybrid inverter unit to enter the grid connection preparation state.

[0063] In the grid connection preparation state, the three-phase hybrid inverter unit obtains the grid phase angle through a phase-locked loop and converts the three-phase AC quantities into the dq coordinate system for control.

[0064] The three-phase mixed grid inverter unit adopts current closed-loop control in the dq coordinate system, where the d-axis current is used to control active power and the q-axis current is used to control reactive power.

[0065] When the q-axis component of the grid voltage is approximately zero, the d-axis current reference value and the q-axis current reference value can be determined by the following formulas:

[0066] in, This is the reference value for the d-axis current. This is the reference value for the q-axis current. This is a reference value for active power. This is a reference value for reactive power. This represents the d-axis component of the grid voltage.

[0067] The active and reactive power of a three-phase mixed-grid inverter unit can be calculated using the following formulas:

[0068] in, Active power Reactive power and These are the d-axis and q-axis components of the grid voltage, respectively. and These are the d-axis and q-axis components of the grid-connected current, respectively.

[0069] When the system is in grid-connected power supply state, if the photovoltaic power is greater than the load power and the energy storage battery does not need to be charged, the three-phase mixed grid inverter unit can output active power to the three-phase grid bus unit; if the photovoltaic power is insufficient and the energy storage state of charge is low, the three-phase mixed grid inverter unit can absorb active power from the three-phase grid bus unit and charge the energy storage bus unit or supply power to the load through the first common DC bus unit.

[0070] When a three-phase power grid bus unit experiences a voltage loss, phase loss, frequency exceeding the limit, voltage distortion exceeding the limit, or islanding fault, the main control unit controls the grid-connected switch to disconnect, and the three-phase mixed-grid inverter unit switches from grid-connected current source control state to off-grid voltage source control state.

[0071] Under off-grid voltage source control, the three-phase hybrid inverter unit outputs a three-phase symmetrical sinusoidal voltage to the three-phase AC load bus unit. The three-phase voltage reference values ​​are as follows:

[0072] in, , , These are the reference values ​​for phase A, phase B, and phase C voltages, respectively. The phase voltage amplitude, This is the internal synchronization angle.

[0073] In this embodiment, the internal synchronization angle is generated by a virtual synchronization control loop. The virtual synchronization control relationship is as follows:

[0074] in, For virtual inertia, The damping coefficient is... The output angular frequency of the three-phase mixed-grid inverter unit. Rated angular frequency, virtual mechanical power. It outputs active power for the three-phase mixed grid inverter unit. This is the internal synchronization angle.

[0075] When the three-phase AC load suddenly increases As the inertia increases, the output frequency of the three-phase hybrid inverter unit will tend to decrease. At this point, the main control unit adjusts the virtual inertia... and damping coefficient This reduces the rate of frequency change and speeds up system recovery. When the load suddenly decreases, the main control unit also adjusts... and Suppress frequency overshoot.

[0076] In a preferred embodiment, when the frequency deviation increases, the main control unit increases the virtual inertia. To enhance the system's immunity to disturbances; when the frequency deviation begins to decrease, the main control unit increases the damping coefficient. In order to shorten the recovery time.

[0077] This embodiment adopts a control strategy of first synchronizing and then closing the circuit when switching from off-grid to on-grid, and first unloading and then disconnecting when switching from on-grid to off-grid.

[0078] 1. Off-grid to in-grid conversion When the three-phase power grid bus unit returns to normal, the main control unit first detects the voltage amplitude difference, frequency difference, and phase difference between the three-phase power grid bus unit and the three-phase AC load bus unit.

[0079] The conditions for switching from off-grid to on-grid are as follows:

[0080] in, This refers to the amplitude of the three-phase power grid bus voltage. This refers to the amplitude of the three-phase AC load bus voltage. For the power grid frequency, The frequency of the load bus. For grid phase, For the load bus phase, The voltage difference threshold that allows grid connection, To allow for a frequency difference threshold for grid connection, The phase difference threshold that allows grid connection.

[0081] When all three conditions are met, the main control unit closes the grid-connected switch. After the grid-connected switch is closed, the three-phase mixed-grid inverter unit gradually switches from off-grid voltage source control to grid-connected current source control.

[0082] 2. Grid-connected to off-grid conversion When an anomaly occurs in the three-phase power grid bus unit, the main control unit first controls the three-phase mixed-network inverter unit to reduce the switching power or switching current at the grid connection switch. When the switching power or switching current is lower than the preset switching threshold, the main control unit controls the grid connection switch to disconnect.

[0083] The conditions for disconnecting from the grid during the transition from grid connection to off-grid are as follows:

[0084] or:

[0085] in, Power is exchanged at the grid connection switch. To exchange current at the grid connection switch, The power threshold that allows disconnection, The current threshold that allows disconnection.

[0086] After the grid-connected switch is disconnected, the three-phase mixed-grid inverter unit maintains the output voltage amplitude, frequency and phase before disconnection as the initial control quantity of the off-grid voltage source control state, thereby reducing the voltage surge of the three-phase AC load bus.

[0087] In this embodiment, the multi-bus coordinated control is performed by the main control unit. The main control unit collects the voltage of the first common DC bus, the voltage of the second DC load bus, the three-phase AC load power, the DC load power, the available photovoltaic power, the energy storage state of charge, and the grid state, and allocates photovoltaic, energy storage, and grid power according to the system power balance.

[0088] The total power of the system load can be expressed as:

[0089] in, The total power of the system load. For three-phase AC load power, This represents the power of the DC load.

[0090] The system power deficit can be expressed as:

[0091] in, For system power deficit, For energy storage charging power, This represents the actual output power of the photovoltaic system. This refers to the power input or output to the power grid.

[0092] when If the power exceeds the preset positive dead zone, it indicates that the system power is insufficient, and the main control unit prioritizes increasing the energy storage discharge power; if the energy storage state of charge is lower than the lower limit, the power is supplemented by the three-phase grid bus unit; if the three-phase grid bus unit is unavailable, the main control unit cuts off non-critical loads according to load priority.

[0093] when If the power is less than the preset negative dead zone, it indicates that the system has excess power, and the main control unit will prioritize increasing the energy storage charging power; if the energy storage state of charge is higher than the upper limit, the photovoltaic DC / DC conversion module will be controlled to reduce the output power.

[0094] when When within the set dead zone, the main control unit maintains the current power distribution state.

[0095] In this embodiment, the load priorities, from highest to lowest, are: critical three-phase AC loads, ordinary three-phase AC loads, critical DC loads, ordinary DC loads, and interruptible loads. When the system power is insufficient or a fault occurs, the main control unit prioritizes ensuring continuous power supply to high-priority loads.

[0096] When an unbalanced load is connected to a three-phase AC load bus unit, negative sequence voltage and neutral current may occur on the three-phase AC load bus. This embodiment improves the power quality of the three-phase AC load bus through a three-phase imbalance compensation module.

[0097] The three-phase imbalance compensation module decomposes the three-phase voltage and three-phase current into positive and negative sequence components based on the data collected by the three-phase AC voltage sampling circuit and the three-phase AC current sampling circuit, thus obtaining the positive sequence voltage component and the negative sequence voltage component.

[0098] The three-phase voltage unbalance can be calculated using the following formula:

[0099] in, This refers to the three-phase voltage imbalance. It is the positive sequence voltage component. It is the negative sequence voltage component.

[0100] When the three-phase voltage imbalance is higher than the preset imbalance threshold, the main control unit generates a negative sequence compensation current command and superimposes the negative sequence compensation current command into the current control loop of the three-phase mixed grid inverter unit, so that the three-phase mixed grid inverter unit outputs the corresponding negative sequence compensation current, thereby reducing the imbalance of the three-phase AC load bus.

[0101] When the system adopts a three-phase four-wire output structure, the three-phase imbalance compensation module also detects the neutral current. When the neutral current is higher than the preset neutral current threshold, the main control unit generates a zero-sequence compensation command to suppress the neutral current through neutral bridge arm, split capacitor midpoint control, or equivalent zero-sequence current control.

[0102] Through the above control method, this embodiment can not only maintain the voltage amplitude stability of the three-phase AC load bus, but also improve the three-phase voltage quality when an unbalanced load is connected.

[0103] The sampling protection unit collects real-time data on voltage, current, power, temperature, insulation status, and switch status of each bus. The main control unit identifies the fault type based on the sampled data and performs fault isolation through the bus interconnection switching unit.

[0104] The fault types in this embodiment include photovoltaic input faults, energy storage faults, first common DC bus faults, second DC load bus faults, three-phase AC output faults, and three-phase power grid faults.

[0105] When a photovoltaic input fault is detected, the main control unit controls the photovoltaic input protection switch to open and the photovoltaic DC / DC conversion module to stop operating. The system continues to be powered by the energy storage bus unit or the three-phase power grid bus unit.

[0106] When an energy storage fault is detected, the main control unit controls the energy storage protection switch to open and prohibits the bidirectional DC / DC converter module from continuing to charge and discharge. If the system is in grid-connected mode at this time, the three-phase grid bus unit and photovoltaic input bus unit continue to supply power; if the system is in off-grid mode, the main control unit cuts off non-critical loads according to load priority.

[0107] When a fault is detected in the second DC load bus, the main control unit controls the DC interconnection switch to disconnect, cutting off only the second DC load bus unit while the first common DC bus unit and the three-phase AC load bus unit continue to operate.

[0108] When a three-phase power grid fault is detected, the main control unit controls the grid-connected switch to disconnect and controls the three-phase mixed-grid inverter unit to enter the off-grid voltage source control state to supply power to the three-phase AC load bus unit.

[0109] When a three-phase AC output fault is detected, the main control unit controls the load switch or the corresponding branch switch to disconnect according to the fault location to isolate the faulty AC branch, while keeping the non-faulty busbars running.

[0110] When a fault is detected in the first common DC bus, the main control unit controls the photovoltaic DC / DC converter module, the bidirectional DC / DC converter module, and the three-phase mixed-grid inverter unit to stop power output and disconnects the interconnection switch associated with the first common DC bus unit to prevent the fault from escalating.

[0111] In the event of no three-phase grid input and a complete system shutdown, if the state of charge of the energy storage bus unit is higher than the black start allowable threshold, the main control unit can execute the black start procedure.

[0112] The black boot process includes the following steps: Step 1: The main control unit detects the energy storage battery voltage, energy storage state of charge, and energy storage protection switch status.

[0113] Step two: The main control unit controls the bidirectional DC / DC converter module to start and slowly boosts the voltage of the first common DC bus unit.

[0114] Step 3: When the voltage of the first common DC bus reaches the start-up threshold of the three-phase mixed-network inverter unit, the main control unit starts the three-phase mixed-network inverter unit.

[0115] Step four: The three-phase mixed-grid inverter unit enters the off-grid voltage source control state and establishes the three-phase AC load bus voltage.

[0116] Step 5: The main control unit connects the three-phase AC load and the second DC load bus in sequence according to the load priority.

[0117] Step 6: When the photovoltaic input conditions meet the startup requirements, the main control unit starts the photovoltaic DC / DC conversion module, enabling the photovoltaic input bus unit to participate in power supply.

[0118] Through the above-described black-start process, this embodiment can establish a DC bus and a three-phase AC bus by the energy storage unit under conditions without an external power grid, thereby achieving off-grid autonomous power supply.

[0119] In a specific operational example, the system is connected to three sets of photovoltaic modules, one set of energy storage batteries, one set of DC loads, one set of three-phase AC loads, and a three-phase power grid. The rated voltage of the first common DC bus is set to 700V, and the rated voltage of the three-phase AC load bus is set to AC380V with a rated frequency of 50Hz.

[0120] During the day, when there is sufficient sunlight and the power grid is normal, the photovoltaic DC / DC converter module operates in maximum power point tracking mode. If the photovoltaic power is greater than the load power, the main control unit prioritizes controlling the bidirectional DC / DC converter module to charge the energy storage battery; if the energy storage battery reaches its upper limit of state of charge, the main control unit reduces the output power of the photovoltaic DC / DC converter module to prevent overvoltage on the first common DC bus.

[0121] When the three-phase AC load suddenly increases, the voltage of the first common DC bus begins to decrease. Upon detecting that the voltage of the first common DC bus is below a preset discharge threshold, the main control unit controls the bidirectional DC / DC converter module to enter a discharge state, whereby the energy storage battery compensates for power to the first common DC bus. Simultaneously, if the system is in grid-connected mode, the three-phase grid-connected inverter unit absorbs some active power from the three-phase grid bus to jointly maintain the stability of the first common DC bus voltage.

[0122] When the three-phase power grid suddenly loses voltage, the main control unit controls the grid-connected switch to disconnect and switches the three-phase mixed-grid inverter unit to off-grid voltage source control mode. After switching, the three-phase mixed-grid inverter unit maintains the three-phase output voltage amplitude, frequency, and phase before disconnection as initial control variables and continues to supply power to the three-phase AC load bus.

[0123] When the three-phase power grid returns to normal, the main control unit executes phase-locked loop control to ensure that the voltage amplitude difference, frequency difference, and phase difference between the three-phase AC load bus and the three-phase power grid bus meet the grid connection conditions. Then, the grid connection switch is closed, and the three-phase mixed-grid inverter unit is gradually switched from off-grid voltage source control state to grid-connected current source control state.

[0124] When a short-circuit fault occurs on the second DC load bus, the main control unit controls the DC tie switch to disconnect, isolating only the second DC load bus. The photovoltaic input bus, energy storage bus, first common DC bus, and three-phase AC load bus can still continue to operate.

[0125] Therefore, this embodiment achieves stable and coordinated operation among multiple energy sources, multiple buses, and multiple loads through a multi-bus structure, three-phase mixed-grid inverter control, bidirectional power regulation of energy storage, DC load bus pre-charge control, grid-connected and off-grid synchronous switching control, and zoned fault isolation control.

[0126] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A multi-bus three-phase hybrid grid inverter integrated system, characterized in that, include: The system includes a photovoltaic input bus unit, an energy storage bus unit, a first common DC bus unit, a second DC load bus unit, a three-phase mixed-network inverter unit, a three-phase AC load bus unit, a three-phase power grid bus unit, a bus tie switching unit, a sampling protection unit, and a main control unit. The photovoltaic input bus unit is connected to the first common DC bus unit through a photovoltaic DC / DC conversion module; The energy storage bus unit is connected to the first common DC bus unit via a bidirectional DC / DC converter module; The second DC load bus unit is connected to the first common DC bus unit via a DC interconnection switch; The DC side of the three-phase mixed-grid inverter unit is connected to the first common DC bus unit, and the AC side of the three-phase mixed-grid inverter unit is connected to the three-phase AC load bus unit through load switches and to the three-phase power grid bus unit through grid connection switches. The bus tie switching unit includes the DC tie switch, the load switch, and the grid connection switch; The sampling protection unit is connected to the photovoltaic input bus unit, the energy storage bus unit, the first common DC bus unit, the second DC load bus unit, the three-phase AC load bus unit, and the three-phase power grid bus unit, respectively, and is used to collect the voltage, current, power, and switch status of each bus. The main control unit is connected to the photovoltaic DC / DC conversion module, the bidirectional DC / DC conversion module, the three-phase mixed-grid inverter unit, the bus tie switching unit, and the sampling protection unit, respectively. It is used to control the working state of the photovoltaic DC / DC conversion module, the bidirectional DC / DC conversion module, the three-phase mixed-grid inverter unit, and the bus tie switching unit according to the data collected by the sampling protection unit, so that the multi-bus three-phase mixed-grid inverter integrated system can switch between grid-connected power supply, off-grid power supply, rectification charging, bypass power supply, and fault isolation states.

2. The multi-bus three-phase mixed grid inverter integrated system according to claim 1, characterized in that, The photovoltaic input bus unit includes at least one photovoltaic input port, a photovoltaic voltage sampling circuit, a photovoltaic current sampling circuit, a reverse connection protection circuit, and an input protection switch; The photovoltaic DC / DC conversion module is controlled by the main control unit and has a maximum power point tracking working state, a constant voltage and current limiting working state, a power limiting working state, and a fault exit working state. When the voltage of the first common DC bus unit is within the normal adjustment range, the photovoltaic DC / DC conversion module operates in maximum power point tracking mode. When the voltage of the first common DC bus unit is higher than the preset power limit threshold, the main control unit controls the photovoltaic DC / DC conversion module to reduce the output power. When the photovoltaic input bus unit experiences an overvoltage, overcurrent, or reverse connection fault, the main control unit controls the input protection switch to open and causes the photovoltaic DC / DC converter module to enter a fault exit working state.

3. The multi-bus three-phase hybrid grid inverter integrated system according to claim 1, characterized in that, The energy storage bus unit includes an energy storage battery interface, a battery voltage sampling circuit, a battery current sampling circuit, a battery temperature sampling circuit, and an energy storage protection switch. The bidirectional DC / DC converter module has charging operation mode, discharging operation mode, float charging operation mode and standby operation mode. When the voltage of the first common DC bus unit is lower than the preset discharge threshold, the main control unit controls the bidirectional DC / DC converter module to enter the discharge working state in order to compensate the power of the first common DC bus unit. When the voltage of the first common DC bus unit is higher than the preset charging threshold and the state of charge of the energy storage bus unit is lower than the preset upper limit, the main control unit controls the bidirectional DC / DC converter module to enter the charging working state. When the state of charge of the energy storage bus unit is higher than the preset upper limit, the main control unit prioritizes controlling the photovoltaic DC / DC conversion module to enter the power-limited working state.

4. The multi-bus three-phase mixed grid inverter integrated system according to claim 1, characterized in that, The first common DC bus unit includes a DC bus capacitor, a bus pre-charge circuit, a bus voltage sampling circuit, a bus current sampling circuit, and DC protection devices; The second DC load bus unit includes a DC load output port, a DC load voltage sampling circuit, and a DC load current sampling circuit; Before closing the DC interconnection switch, the main control unit first controls the bus pre-charging circuit to pre-charge the second DC load bus unit, and controls the DC interconnection switch to close after the voltage difference between the first common DC bus unit and the second DC load bus unit is less than a preset voltage difference threshold. Before disconnecting the DC-DC interconnection switch, the main control unit first reduces the current flowing through the DC-DC interconnection switch, and then controls the DC-DC interconnection switch to disconnect after the current is less than a preset disconnection threshold.

5. The multi-bus three-phase mixed grid inverter integrated system according to claim 1, characterized in that, The three-phase mixed-grid inverter unit includes a three-phase power bridge, an AC filter inductor, an AC filter capacitor, a three-phase AC voltage sampling circuit, a three-phase AC current sampling circuit, and a drive protection circuit. The three-phase grid-connected inverter unit operates in grid-connected current source control state when the three-phase grid bus unit is normal, and is used to output or absorb power to the three-phase grid bus unit according to the active power command and reactive power command given by the main control unit. The three-phase mixed-grid inverter unit operates in off-grid voltage source control state when the three-phase grid bus unit is abnormal, and is used to provide three-phase AC voltage to the three-phase AC load bus unit. In the rectified charging state, the three-phase hybrid inverter unit absorbs AC power from the three-phase power grid bus unit and charges the energy storage bus unit through the first common DC bus unit.

6. The multi-bus three-phase hybrid grid inverter integrated system according to claim 5, characterized in that, The main control unit includes a grid-connected / offline switching control module; When switching from off-grid to on-grid, the on-grid switching control module first detects the voltage amplitude difference, frequency difference, and phase difference between the three-phase AC load bus unit and the three-phase power grid bus unit, and controls the grid connection switch to close after the voltage amplitude difference, frequency difference, and phase difference all meet the preset grid connection conditions. When switching from grid connection to off-grid, the grid-connected switching control module first controls the three-phase mixed-grid inverter unit to reduce the switching power or switching current at the grid connection switch, and then controls the grid connection switch to disconnect after the switching power or switching current is lower than the preset switching threshold. After the grid-connected switch is disconnected, the three-phase mixed-grid inverter unit retains the output voltage amplitude, frequency and phase before disconnection as the initial control variables for the off-grid voltage source control state.

7. The multi-bus three-phase hybrid grid inverter integrated system according to claim 5, characterized in that, The main control unit includes a three-phase imbalance compensation module; The three-phase imbalance compensation module extracts the positive sequence component and negative sequence component of the three-phase AC load bus unit based on the data collected by the three-phase AC voltage sampling circuit and the three-phase AC current sampling circuit. When the voltage imbalance of the three-phase AC load bus unit is higher than the preset imbalance threshold, the three-phase imbalance compensation module generates a negative sequence compensation current command and superimposes the negative sequence compensation current command into the current control loop of the three-phase mixed-network inverter unit to reduce the voltage imbalance of the three-phase AC load bus unit. When the three-phase AC load bus unit is a three-phase four-wire output structure, the three-phase unbalance compensation module also generates a zero-sequence compensation command based on the neutral current to suppress the neutral current.

8. The multi-bus three-phase hybrid grid inverter integrated system according to claim 1, characterized in that, The main control unit includes a fault isolation control module; The fault isolation control module identifies photovoltaic input faults, energy storage faults, first common DC bus faults, second DC load bus faults, three-phase AC output faults, and three-phase power grid faults based on the data collected by the sampling protection unit. When a photovoltaic input fault is detected, the fault isolation control module controls the photovoltaic input bus unit to exit operation; When an energy storage fault is detected, the fault isolation control module controls the energy storage protection switch to disconnect. When a fault is detected in the second DC load bus, the fault isolation control module controls the DC interconnection switch to disconnect. When a three-phase power grid fault is detected, the fault isolation control module controls the grid-connected switch to open and controls the three-phase mixed-grid inverter unit to enter the off-grid voltage source control state. When a three-phase AC output fault is detected, the fault isolation control module controls the load switch or the corresponding branch switch to disconnect according to the load priority, so as to keep the non-faulty busbar running.

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