Off-grid and grid-connected switching control method and power converter

Abstract

The invention discloses an off-grid and grid-connected switching control method and a power converter, the alternating current side of the power converter is provided with a first energy port and a second energy port, the first energy port is connected with a power grid, the second energy port is connected with a standby generator, and the standby generator is connected with the power grid according to the states of the first energy port and the second energy port. Determining a target operation state of the power converter, and controlling a target energy port corresponding to the target operation state to be conducted under the condition that the target operation state is a power grid grid-connected operation state or a standby generator grid-connected operation state, the flexible seamless switching of the power converter among the grid-connected operation state of the power grid, the grid-connected operation state of the standby generator and the off-grid operation state is realized.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to an off-grid / on-grid switching control method and a power converter. Background Technology

[0002] A single-phase household energy storage platform's grid connection port can only be connected to either a standby generator or the power grid. In areas with a stable power grid, the connection port is connected to the grid, and the grid supplies power to the AC loads. In areas with an unstable power grid or no power grid, the single-phase household energy storage platform's grid connection port is connected to a standby generator. When the battery's state of charge (SOC) is insufficient, the standby generator is started, switching from off-grid operation to grid-connected operation. The standby generator prioritizes supplying power to AC loads, and excess power can be used to charge the battery.

[0003] However, since the grid connection port of a single-phase household energy storage platform can only be connected to one of the backup generator and the power grid, it has poor flexibility. When it is necessary to change the connection object of the grid connection port, it can only be switched manually, which is inefficient. Summary of the Invention

[0004] In view of this, this application provides an on-grid and off-grid switching control method and a power converter to realize flexible and seamless switching of the power converter between grid-connected operation, standby generator grid-connected operation and off-grid operation.

[0005] To solve the above problems, the technical solution provided in this application is as follows:

[0006] The first aspect of this application provides a method for switching control between grid-connected and off-grid locations, including:

[0007] The status of a first energy port and a second energy port of a power converter is obtained, wherein the first energy port is used to connect to the power grid and the second energy port is used to connect to a standby generator; the power converter further includes an AC load port and a power conversion circuit; the AC side of the power conversion circuit is connected to the first energy port and the second energy port respectively; the AC load port is used to connect an AC load;

[0008] Based on the states of the first energy port and the second energy port, the target operating state of the power converter is determined, wherein the target operating state is either grid-connected operation, standby generator grid-connected operation, or off-grid operation.

[0009] When the target operating state is either grid-connected or standby generator grid-connected, the target energy port corresponding to the target operating state is turned on, wherein the target energy port corresponding to the grid-connected operating state is the first energy port, and the target energy port corresponding to the standby generator grid-connected operating state is the second energy port.

[0010] In one possible implementation, determining the target operating state of the power converter based on the states of the first energy port and the second energy port includes:

[0011] If the state of the first energy port is abnormal when the power converter is in grid-connected operation;

[0012] or,

[0013] If the second energy port is in an abnormal state or the first energy port recovers from an abnormal state to a normal state when the power converter is in standby generator grid-connected operation state, then the target operating state is determined to be off-grid operation state.

[0014] In one possible implementation, the off-grid / on-grid switching control method further includes:

[0015] When the power converter switches from grid-connected operation or standby generator grid-connected operation to off-grid operation, the inverter control loop of the power converter is switched to off-grid control.

[0016] The AC side electrical parameters of the power converter are synchronized with the off-grid operation electrical parameters;

[0017] The target energy port is controlled to disconnect at the zero-crossing point of the AC voltage, and the DC power supply connected to the DC side of the power converter supplies power to the AC load connected to the AC load port.

[0018] In one possible implementation, determining the target operating state of the power converter based on the states of the first energy port and the second energy port includes:

[0019] If the first energy port recovers from an abnormal state to a normal state when the power converter is in an off-grid operation state, then the target operation state is determined to be a grid-connected operation state.

[0020] or,

[0021] If the first energy port is in an abnormal state and the second energy port recovers from the abnormal state to the normal state when the power converter is in an off-grid operation state, then the target operation state is determined to be the standby generator grid-connected operation state.

[0022] In one possible implementation, controlling the target energy port corresponding to the target operating state to be turned on includes:

[0023] When the power converter switches from off-grid operation to grid-connected operation or standby generator grid-connected operation, the AC side electrical parameters of the power converter are synchronized with the electrical parameters of the target energy port.

[0024] The target energy port is controlled to conduct at the zero-crossing point of the AC voltage.

[0025] In one possible implementation, after the power converter system is initialized, determining the target operating state of the power converter based on the states of the first energy port and the second energy port includes:

[0026] If the first energy port and the second energy port are in normal condition, the target operating state is determined to be the grid-connected operating state.

[0027] If the state of the first energy port is abnormal and the state of the second energy port is normal, the target operating state is determined to be the standby generator grid-connected operating state.

[0028] If both the first energy port and the second energy port are in an abnormal state, the target operating state is determined to be an off-grid operating state.

[0029] In one possible implementation, after the power converter system is initialized, the grid-connected / off-grid switching control method further includes:

[0030] When the voltage at the first energy port is greater than a preset voltage value and the second energy port is disconnected, the state of the first energy port is obtained;

[0031] If the first energy port is in a normal state, then control the first energy port to be turned on;

[0032] Timing begins when the voltage at the first energy port is not greater than a preset voltage value or when the second energy port is turned on.

[0033] If the first energy port is disconnected and the voltage of the second energy port is greater than a preset voltage value and the timing duration is greater than a first preset duration, then control the second energy port to be turned on;

[0034] If the first energy port is turned on, or the voltage of the second energy port is not greater than a preset voltage value, or the timing duration is not greater than a first preset duration, then when the timing duration is greater than a second preset duration, the first energy port and the second energy port are controlled to be disconnected, and the DC power supply connected to the DC side of the power converter supplies power to the AC load connected to the AC load port.

[0035] In one possible implementation, the power converter further includes a target relay for controlling the target energy port to be turned on or off, and the off-grid / on-line switching control method further includes:

[0036] When the target relay is not activated and the voltage at the AC load port is greater than a preset voltage value, the voltage parameters of the AC load port and the target energy port are obtained;

[0037] If the voltage parameters of the AC load port and the target energy port are consistent, then the target relay fault signal is output.

[0038] A second aspect of this application provides a power converter, including: a controller, a power conversion circuit, and an AC load port;

[0039] The DC side of the power conversion circuit is connected to a DC power supply.

[0040] The AC side of the power conversion circuit is connected to the first energy port and the second energy port, respectively.

[0041] The first energy port is used to connect to the power grid, the second energy port is used to connect to the standby generator, and the AC load port is used to connect to the AC load.

[0042] The controller executes the off-grid / on-grid switching control method of any of the implementations of the first aspect described above.

[0043] In one possible implementation, the DC power source includes at least one of a photovoltaic power source and a battery power source.

[0044] In one possible implementation, the power converter further includes a relay drive circuit, which includes a grid relay drive branch and a generator relay drive branch.

[0045] The power grid relay drive branch is used to control the first energy port to be turned on or off.

[0046] The generator relay drive branch is used to control the second energy port to be turned on or off.

[0047] The drive signal of the power grid relay is connected to the base circuit of the transistor in the generator relay drive branch. When the drive signal is low, the base of the transistor in the generator relay drive branch is pulled low.

[0048] In one possible implementation, the power converter further includes a dual-coil mechanical interlock relay;

[0049] The two sets of coils of the dual-coil mechanical interlock relay are used to control the grid-side contacts and the generator-side contacts respectively. At the same time, only one contact of the grid-side contacts and the generator-side contacts is closed.

[0050] When the grid side triggers a closure, the first energy port is turned on.

[0051] When the generator-side contacts are closed, the second energy port is turned on.

[0052] This application provides an off-grid switching control method and a power converter. A first energy port and a second energy port are provided on the AC side of the power converter. The first energy port is connected to the power grid, and the second energy port is connected to a standby generator. Based on the states of the first and second energy ports, a target operating state of the power converter is determined. When the target operating state is either grid-connected or standby generator-connected, the target energy port corresponding to the target operating state is turned on, thereby enabling flexible and seamless switching of the power converter between grid-connected, standby generator-connected, and off-grid operating states. Attached Figure Description

[0053] Figure 1 A flowchart illustrating a grid-connected / off-grid switching control method provided in an embodiment of this application;

[0054] Figure 2 This is a schematic diagram of the power converter's operating state transition provided in an embodiment of this application;

[0055] Figure 3 A power converter AC side relay topology diagram provided in the embodiments of this application;

[0056] Figure 4 This is a partial flowchart illustrating a grid-connected / off-grid switching control method provided in an embodiment of this application.

[0057] Figure 5 This is a schematic diagram of the grid connection and disconnection process provided in an embodiment of this application;

[0058] Figure 6 This is a schematic diagram of the off-grid to on-grid switching process provided in an embodiment of this application;

[0059] Figure 7 This is a schematic diagram of a relay fault detection method provided in an embodiment of this application;

[0060] Figure 8 Another power converter AC side relay topology provided for embodiments of this application. Detailed Implementation

[0061] The embodiments of this application are described below with reference to the accompanying drawings. The terminology used in the implementation section of this application is for explaining specific embodiments only and is not intended to limit the scope of this application.

[0062] The embodiments of this application will now be described with reference to the accompanying drawings. Those skilled in the art will recognize that, with technological advancements and the emergence of new scenarios, the technical solutions provided in the embodiments of this application are equally applicable to similar technical problems.

[0063] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms are interchangeable where appropriate; this is merely a way of distinguishing objects with the same attributes in the embodiments of this application. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, so that a process, method, system, product, or apparatus that comprises a series of elements is not necessarily limited to those elements, but may include other elements not explicitly listed or inherent to those processes, methods, products, or apparatuses.

[0064] This application provides an off-grid / parallel switching control method applied to a controller in a power converter. The power converter can be an inverter, energy storage converter, etc. The power converter also includes a power conversion circuit and an AC load port. The AC side of the power converter is connected to a first energy port and a second energy port, respectively. The first energy port is used to connect to the power grid, the second energy port is used to connect to a standby generator, and the AC load port is used to connect to an AC load. The off-grid / parallel switching control method of this application embodiment will be described in detail below with reference to the accompanying drawings.

[0065] Reference Figure 1 , Figure 1 This is a flowchart illustrating a grid-connected / off-grid switching control method provided in an embodiment of this application, as shown below. Figure 1 As shown in the embodiment of this application, a grid-connected / off-grid switching control method may include steps 101-103, which are described in detail below.

[0066] 101: Obtain the status of the first and second energy ports of the power converter.

[0067] The first energy port is used to connect to the power grid, and the second energy port is used to connect to a backup generator, which can be a diesel generator or other household generator.

[0068] The states of the first and second energy ports include: normal and abnormal.

[0069] The states of the first and second energy ports are determined based on their electrical parameters, including voltage and frequency.

[0070] For example, if the voltage of the first energy port is greater than the grid undervoltage protection recovery value but less than the voltage overvoltage protection recovery value, and the frequency of the first energy port is greater than the grid underfrequency recovery value but less than the grid overfrequency recovery value, and remains at the first target duration (e.g., 3 seconds), then the state of the first energy port is normal. The grid over / undervoltage and over / underfrequency protection ranges are issued by the ARM in the power converter, and these ranges vary depending on the country and region.

[0071] If the voltage of the second energy port is greater than the undervoltage protection recovery value of the standby generator but less than the overvoltage protection recovery value, and the frequency of the second energy port is greater than the underfrequency recovery value of the standby generator but less than the overfrequency recovery value, and remains at the second target duration (the second target duration is longer than the first target duration to ensure grid priority), then the second energy port is considered to be in normal condition. The overvoltage and undervoltage protection ranges for the standby generator are set according to the actual application scenario. For example, the overvoltage protection range for the standby generator is 0.8 to 1.2 times the rated grid voltage, and the overfrequency protection range is 45Hz to 65.9Hz. When the voltage of the second energy port is greater than 0.8 times the rated grid voltage +10V and less than 1.2 times the rated grid voltage -10V, the voltage of the second energy port is determined to meet the connection conditions; when the frequency of the second energy port is greater than 45.2Hz and less than 65.7Hz, the frequency of the second energy port is determined to meet the connection conditions; when both the voltage and frequency meet the connection conditions and remain at the second target duration, the second energy port is considered to be in normal condition.

[0072] After the power converter system is initialized, in order to ensure that the power converter is preferentially connected to the grid if the status of the first energy port is normal, the status of the first energy port can be obtained first, and then the status of the second energy port can be obtained. Since the detection time before grid connection is relatively long, the time to obtain the status of the second energy port can be the time to obtain the status of the first energy port + 4 seconds.

[0073] In one possible implementation, when the power converter is in standby generator grid-connected operation, the over / under voltage and over / under frequency protection ranges of the power grid are relaxed. This allows the power converter to connect to the grid more quickly after the first energy port recovers from an abnormal state to a normal state, ensuring the grid priority principle. When the power converter is in standby generator grid-connected operation, grid-related functions such as pre-connection detection, under-frequency derating, and over-frequency derating can also be disabled to prevent these functions from affecting the power dispatch of the standby generator. After the second energy port is closed, the grid over / under voltage and over / under frequency protection ranges are restored, and grid-related functions such as pre-connection detection, under-frequency derating, and over-frequency derating are enabled again.

[0074] 102: Determine the target operating state of the power converter based on the states of the first energy port and the second energy port.

[0075] The target operating state is either grid-connected operation, standby generator grid-connected operation, or off-grid operation.

[0076] To ensure that the power converter is preferentially connected to the grid when the first energy port is in a normal state, in one possible implementation, after the power converter system is initialized, if both the first and second energy ports are in a normal state, the target operating state is determined to be grid-connected operation; if the first energy port is in an abnormal state and the second energy port is in a normal state, the target operating state is determined to be standby generator grid-connected operation; if both the first and second energy ports are in an abnormal state, the target operating state is determined to be off-grid operation.

[0077] During the operation of the power converter, the target operating state needs to be determined based on the operating status of the power converter and the status of the first and second energy ports to ensure that the AC load ports do not lose power during the off-grid switching, so as to continuously supply power to the AC load and ensure the user's power safety.

[0078] 103: When the target operating state is grid-connected operation or standby generator grid-connected operation, control the target energy port corresponding to the target operating state to be turned on.

[0079] Among them, the target energy port corresponding to the grid-connected operation state is the first energy port, and the target energy port corresponding to the standby generator grid-connected operation state is the second energy port.

[0080] This embodiment provides an off-grid switching control method, which sets a first energy port and a second energy port on the AC side of a power converter. The first energy port is connected to the power grid, and the second energy port is connected to a standby generator. Based on the status of the first energy port and the second energy port, the target operating state of the power converter is determined. When the target operating state is the grid-connected operating state or the standby generator grid-connected operating state, the target energy port corresponding to the target operating state is controlled to be turned on, so as to realize the flexible and seamless switching of the power converter between the grid-connected operating state, the standby generator grid-connected operating state, and the off-grid operating state.

[0081] During normal operation of the power converter, if the first energy port malfunctions while the power converter is in grid-connected mode, and the DC-side energy port (photovoltaic energy port or battery energy port) is functioning normally, the target operating state is determined to be off-grid operation. The first energy port is then disconnected, and the energy from the DC power supply connected to the DC-side energy port flows to the AC load, ensuring that the AC load does not lose power. If the DC power supply includes photovoltaic power generation equipment and energy storage batteries, then the energy from the photovoltaic power generation equipment can flow to both the AC load and the energy storage batteries.

[0082] Considering that the backup generator or grid connection requires synchronization of electrical parameters (such as voltage, frequency and phase), if the switch is directly made to the backup generator for grid connection, the electrical parameters on the AC side of the power converter may not match the electrical parameters of the second energy port, which may lead to equipment damage or system oscillation. Therefore, if the first energy port is abnormal when the power converter is in grid-connected operation, even if the second energy port is normal, the power converter should be switched to off-grid operation first.

[0083] Similarly, to avoid the mismatch between the AC side electrical parameters of the power converter and the electrical parameters of the first energy port when switching directly from standby generator grid connection to grid connection, if the second energy port is abnormal or the first energy port recovers from abnormal to normal operation when the power converter is in standby generator grid connection operation state, the target operating state of the power converter is determined to be off-grid operation state, the second energy port is disconnected, and the energy of the DC power supply connected to the DC side energy port is directed to the AC load to ensure that the AC load does not lose power.

[0084] In one possible implementation, when the power converter switches from grid-connected or standby generator-connected operation to off-grid operation, the inverter control loop of the power converter is switched to off-grid control. This synchronizes the AC-side electrical parameters of the power converter with the off-grid operation parameters, and the target energy port is disconnected at the zero-crossing point of the AC voltage. The DC power supply connected to the DC side of the power converter then supplies power to the AC load. Specifically, when switching from grid-connected to off-grid operation, the target energy port is the first energy port; when switching from standby generator-connected to off-grid operation, the target energy port is the second energy port. Since the voltage and current at the target energy port are close to zero at the zero-crossing point of the AC voltage, voltage and current surges are effectively reduced, ensuring a smooth system transition.

[0085] During normal operation of the power converter, if the first energy port recovers from an abnormal state to a normal state when the power converter is in an off-grid operation state, the target operating state of the power converter is determined to be the grid-connected operation state. The first energy port is then turned on to ensure that the system generates and consumes its own electricity and feeds the surplus electricity to the grid.

[0086] When the power converter is in off-grid operation, if the status of the first energy port is abnormal and the second energy port recovers from abnormal status to normal status, the target operating status of the power converter is determined to be the standby generator grid-connected operation status. The second energy port is controlled to be turned on to ensure that the AC load does not lose power while the surplus power charges the battery to keep the battery fully charged.

[0087] In one possible implementation, when the power converter switches from off-grid operation to grid-connected operation or standby generator grid-connected operation, the AC side electrical parameters of the power converter are synchronized with the electrical parameters of the target energy port, and the target energy port is controlled to conduct at the AC voltage zero-crossing point. Specifically, when the power converter switches from off-grid to grid-connected operation, the target energy port is the first energy port; when switching from off-grid to standby generator grid-connected operation, the target energy port is the second energy port. Since the voltage and current at the target energy port are close to zero at the AC voltage zero-crossing point, voltage and current surges are effectively reduced, ensuring a smooth system transition.

[0088] Please see Figure 2 The diagram illustrates the power converter's operational state transitions. After power-on and system initialization, the system monitors the electrical parameters (such as voltage, frequency, and phase synchronization) of the first energy port connected to the grid and the second energy port connected to the standby generator in real time to determine their states. Grid priority is given. When the first energy port is normal, grid-connected startup is executed. During startup, the inverter duty cycle is calculated based on the phase and amplitude of the grid voltage to ensure the inverter voltage (AC side voltage) phase matches the grid voltage phase and amplitude, avoiding large current surges when the inverter relay is activated. After grid-connected operation, both inverter power and rectified power are unrestricted. If the first energy port is abnormal but the second energy port is normal, standby generator grid-connected startup is executed. The inverter duty cycle is calculated based on the phase and amplitude of the standby generator voltage. After grid-connected operation, zero power is fed to the standby generator, and rectified power is unrestricted. If both the first and second energy ports are abnormal, but the DC side energy port (photovoltaic or battery energy port) is normal, off-grid startup is executed, allowing AC load operation.

[0089] When the grid is connected to the grid: If the first energy port is abnormal, and the DC power supply port is normal, the grid connection operation will be switched to the off-grid operation operation. At this time, the energy of the DC power supply will flow to the AC load to ensure that the AC load does not lose power.

[0090] When the standby generator is running in grid-connected mode: if the second energy port is abnormal or the first energy port returns to normal, and if the DC power supply port is normal, the generator will switch from grid-connected to off-grid mode. At this time, the DC power supply will flow to the AC load.

[0091] Off-grid operation: If the status of the first energy port returns to normal, the power converter switches from off-grid operation to grid-connected operation to ensure the system's self-consumption and the sale of surplus power to the grid. During the switching process, the inverter voltage is first pre-synchronized with the grid voltage phase, and then the grid-connected relay is activated.

[0092] Off-grid operation: If the second energy port status returns to normal, the power converter switches from off-grid operation to standby generator grid-connected operation, ensuring that the AC load does not lose power while the remaining power charges the battery, keeping the battery fully charged. During the switching process, the inverter voltage first pre-synchronizes with the standby generator voltage phase, and then the multi-function port relay is activated.

[0093] Taking a diesel generator as an example, please refer to [link / reference]. Figure 3 The diagram shows the relay topology of the AC side of the power converter. Figure 3 The grid connection port is the first energy port mentioned above, and the diesel generator port is the second energy port mentioned above. The diesel generator port and the grid connection port are only isolated by a relay. If the diesel generator relay and the grid relay are activated at the same time, it is equivalent to directly connecting the diesel generator to the grid. It is very likely that circulating current or inrush current will be generated due to the inconsistency of phase, frequency and voltage between the grid and the diesel generator, which will lead to equipment overload, overheating or even damage.

[0094] To ensure that only one of the first and second energy ports is active at any given time, preventing circulating current or equipment damage caused by simultaneous connection of the power converter to the grid and a standby generator, please refer to [link to relevant documentation] after the power converter system initialization. Figure 4 One implementation of step 102 in the above embodiments includes the following steps 401-406:

[0095] 401: Is the voltage at the first energy port greater than the preset voltage value and the second energy port disconnected?

[0096] The voltage at the first energy port is greater than the preset voltage value (e.g., 140V) and the second energy port is disconnected (in standby power generation mode and the generator relay is not activated, or in non-standby power generation mode). This indicates that the grid status meets the basic conditions for grid connection, while the standby generator status does not meet the basic conditions for grid connection.

[0097] If the voltage at the first energy port is greater than the preset voltage value and the second energy port is disconnected, then proceed to step 402.

[0098] If the voltage of the first energy port is not greater than the preset voltage value or the second energy port is turned on, then proceed to step 403.

[0099] 402: Obtain the status of the first energy port. If the status of the first energy port is normal, control the first energy port to be turned on.

[0100] That is, if the grid status meets the basic conditions for grid connection, but the standby generator does not meet the basic conditions for grid connection, and the status of the first energy port is further detected to be normal, thus meeting the grid connection conditions, the power converter is put into grid-connected operation state by controlling the first energy port to be turned on.

[0101] 403: Start timing.

[0102] By continuously monitoring the first energy port being disconnected and the voltage of the second energy port being greater than a preset voltage value through timing, this condition is ensured to be continuously met, avoiding malfunctions caused by short-term fluctuations.

[0103] 404: Is the first energy port disconnected and the voltage of the second energy port greater than the preset voltage value and the timing duration greater than the first preset duration?

[0104] The following conditions indicate that the standby generator status continuously meets the basic grid connection conditions, while the grid status does not meet the basic grid connection conditions: the first energy port is disconnected and the voltage of the second energy port is greater than the preset voltage value (e.g., 140V) and the timing duration is greater than the first preset duration (e.g., 900ms).

[0105] If the first energy port is disconnected and the voltage of the second energy port is greater than the preset voltage value and the timing duration is greater than the first preset duration, then step 405 is executed.

[0106] If the first energy port is turned on, or the voltage of the second energy port is not greater than the preset voltage value, or the timing duration is not greater than the first preset duration, then step 406 is executed.

[0107] 405: Control the second energy port to turn on.

[0108] The second energy port is turned on to start the standby generator and put the power converter into standby generator grid-connected operation mode.

[0109] 406: When the timing duration exceeds the second preset duration, the first energy port and the second energy port are disconnected, and the DC power supply connected to the DC side of the power converter supplies power to the AC load.

[0110] The second preset duration is longer than the first preset duration; for example, the second preset duration can be 10 seconds. When the timing duration exceeds the second preset duration, the time indicating that the standby generator does not meet the basic grid connection conditions has expired. In this case, the first energy port and the second energy port are disconnected, and off-grid startup is performed, putting the power converter into off-grid operation mode.

[0111] During the operation of the power converter, the grid-connected and off-grid switching process is as follows: Figure 5 As shown, when switching from grid connection to off-grid, the grid connection type is not determined, and both the generator relay and the grid relay are disconnected. The process for switching from off-grid to grid connection is as follows: Figure 6 As shown, when switching from off-grid to grid-connected operation, the grid status is judged first. If the grid meets the grid connection requirements (i.e., the first energy port above recovers from an abnormal state to a normal state), the off-grid operation switches to grid connection, and the grid relay is activated. If there is no power at the grid port or the grid does not meet the grid connection requirements, and the standby generator meets the grid connection requirements (i.e., the second energy port above recovers from an abnormal state to a normal state), the off-grid operation switches to standby generator connection, and the generator relay is activated.

[0112] When switching between the three states of standby generator microgrid operation (i.e., standby generator grid-connected operation), grid-connected operation, and off-grid operation, the switching in or out of the grid or standby generator is controlled only by controlling the opening and closing of the grid relay and generator relay. However, the power converter will not block the waveform, ensuring that the AC load port is uninterrupted and improving the user's power experience.

[0113] Furthermore, to ensure that the aforementioned generator relay or grid relay sticking can be detected in a timely manner, and to prevent the grid relay and generator relay from being simultaneously engaged due to relay failure, thus causing damage to the standby generator or electrical equipment, such as... Figure 7 As shown, when the target relay used to control the on / off state of the target energy port is not activated and the AC load port voltage is greater than a preset voltage value (e.g., 140V), the voltage parameters (e.g., amplitude, phase) of the AC load port and the target energy port are acquired. If the voltage parameters of the AC load port and the target energy port are consistent, a target relay fault signal is output. After outputting the target relay fault signal, the power converter is shut down, and all relays are disconnected to ensure customer power safety. Specifically, if the target energy port is the first energy port, the target relay is a grid relay; if the target energy port is the second energy port, the target relay is a generator relay.

[0114] This application also provides a power converter, including: a controller, a power conversion circuit, and an AC load port.

[0115] The DC side of the power conversion circuit is connected to a DC power supply;

[0116] The AC side of the power conversion circuit is connected to the first energy port and the second energy port respectively;

[0117] The first energy port is used to connect to the power grid, the second energy port is used to connect to the standby generator, and the AC load port is used to connect to the AC load.

[0118] The controller executes any of the off-grid / parallel switching control methods provided in the embodiments of this application.

[0119] In one possible implementation, the DC power source includes at least one of photovoltaic power and battery power.

[0120] In one possible implementation, the power converter further includes a relay drive circuit, comprising a grid relay drive branch and a generator relay drive branch. The grid relay drive branch controls the first energy port to be turned on or off, and the generator relay drive branch controls the second energy port to be turned on or off. The grid relay drive signal Grid_Rly_On is connected to the base circuit of the transistor in the generator relay drive branch. When the drive signal Grid_Rly_On is low (indicating that the grid relay is energized), the hardware circuit forcibly pulls the base of the transistor in the generator relay drive branch low. Even if the generator relay drive signal is received, the transistor in the generator relay drive branch cannot be turned on, and the generator relay cannot be energized.

[0121] The relay drive circuit in this embodiment can be used in conjunction with... Figures 4-6 The software interlocking method in the text achieves reliable driver-level interlocking.

[0122] In one possible implementation, the power converter also includes a dual-coil mechanical interlock relay. The two sets of coils of the dual-coil mechanical interlock relay are used to control the grid-side contacts and the generator-side contacts, respectively. Only one contact can be closed at a time. When the grid-side contacts are triggered and closed, the first energy port is activated; when the generator-side contacts are closed, the second energy port is activated. The mechanical design of the dual-coil mechanical interlock relay ensures that its internal contacts cannot be physically connected to both the grid and the standby generator simultaneously. (See also...) Figure 8The diagram shows the AC side relay topology of the power converter. The dual-coil mechanical interlock relay includes coils KM11 and KM21. Coil KM11 controls the generator-side main contact KM13. When coil KM11 is energized, it controls the main contact KM13 to close, opening the generator port. Simultaneously, the normally closed contact KM12 opens, cutting off the power supply to coil KM21 and preventing accidental activation of main contact KM23. Coil KM21 controls the grid-side main contact KM23. When coil KM21 is energized, it controls the main contact KM23 to close, opening the grid port. Simultaneously, the normally closed contact KM22 opens, cutting off the power supply to coil KM11 and preventing accidental activation of main contact KM13. Additionally, switches S1 and S2 can control the activation of KM13 and KM23 respectively, enabling manual switching.

[0123] In one possible implementation, the power converter includes the aforementioned relay drive circuit and a dual-coil mechanical interlock relay to achieve multiple interlocking mechanisms and higher reliability.

[0124] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).

[0125] This application also provides a readable storage medium for storing the off-grid / parallel switching control method provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (Electronic Programmable ROM), registers, hard disks, removable disks, or any other form of storage medium in the art.

[0126] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the product embodiments disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the description of the product embodiments.

[0127] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for switching control between grid-connected and off-grid environments, characterized in that, include: The status of a first energy port and a second energy port of a power converter is obtained, wherein the first energy port is used to connect to the power grid and the second energy port is used to connect to a standby generator; the power converter further includes an AC load port and a power conversion circuit; the AC side of the power conversion circuit is connected to the first energy port and the second energy port respectively; the AC load port is used to connect an AC load; Based on the states of the first energy port and the second energy port, the target operating state of the power converter is determined, wherein the target operating state is either grid-connected operation, standby generator grid-connected operation, or off-grid operation. When the target operating state is either grid-connected or standby generator grid-connected, the target energy port corresponding to the target operating state is turned on, wherein the target energy port corresponding to the grid-connected operating state is the first energy port, and the target energy port corresponding to the standby generator grid-connected operating state is the second energy port.

2. The off-grid / parallel switching control method according to claim 1, characterized in that, Determining the target operating state of the power converter based on the states of the first energy port and the second energy port includes: If the state of the first energy port is abnormal when the power converter is in grid-connected operation; or, If the second energy port is in an abnormal state or the first energy port recovers from an abnormal state to a normal state when the power converter is in standby generator grid-connected operation state, then the target operating state is determined to be off-grid operation state.

3. The off-grid / parallel switching control method according to claim 2, characterized in that, The off-grid / on-grid switching control method further includes: When the power converter switches from grid-connected operation or standby generator grid-connected operation to off-grid operation, the inverter control loop of the power converter is switched to off-grid control. The AC side electrical parameters of the power converter are synchronized with the off-grid operation electrical parameters; The target energy port is controlled to disconnect at the zero-crossing point of the AC voltage, and the DC power supply connected to the DC side of the power converter supplies power to the AC load connected to the AC load port.

4. The off-grid / parallel switching control method according to claim 1, characterized in that, Determining the target operating state of the power converter based on the states of the first energy port and the second energy port includes: If the first energy port recovers from an abnormal state to a normal state when the power converter is in an off-grid operation state, then the target operation state is determined to be a grid-connected operation state. or, If the first energy port is in an abnormal state and the second energy port recovers from the abnormal state to the normal state when the power converter is in an off-grid operation state, then the target operation state is determined to be the standby generator grid-connected operation state.

5. The off-grid / parallel switching control method according to claim 4, characterized in that, The control of the target energy port corresponding to the target operating state to be turned on includes: When the power converter switches from off-grid operation to grid-connected operation or standby generator grid-connected operation, the AC side electrical parameters of the power converter are synchronized with the electrical parameters of the target energy port. The target energy port is controlled to conduct at the zero-crossing point of the AC voltage.

6. The off-grid / parallel switching control method according to claim 1, characterized in that, After the power converter system is initialized, determining the target operating state of the power converter based on the states of the first energy port and the second energy port includes: If the first energy port and the second energy port are in normal condition, the target operating state is determined to be the grid-connected operating state. If the state of the first energy port is abnormal and the state of the second energy port is normal, the target operating state is determined to be the standby generator grid-connected operating state. If both the first energy port and the second energy port are in an abnormal state, the target operating state is determined to be an off-grid operating state.

7. The off-grid / parallel switching control method according to claim 1, characterized in that, After the power converter system is initialized, the off-grid / on-grid switching control method further includes: When the voltage at the first energy port is greater than a preset voltage value and the second energy port is disconnected, the state of the first energy port is obtained; If the first energy port is in a normal state, then control the first energy port to be turned on; Timing begins when the voltage at the first energy port is not greater than a preset voltage value or when the second energy port is turned on. If the first energy port is disconnected and the voltage of the second energy port is greater than a preset voltage value and the timing duration is greater than a first preset duration, then control the second energy port to be turned on; If the first energy port is turned on, or the voltage of the second energy port is not greater than a preset voltage value, or the timing duration is not greater than a first preset duration, then when the timing duration is greater than a second preset duration, the first energy port and the second energy port are controlled to be disconnected, and the DC power supply connected to the DC side of the power converter supplies power to the AC load connected to the AC load port.

8. The off-grid / parallel switching control method according to claim 1, characterized in that, The power converter further includes a target relay, which is used to control the target energy port to be turned on or off. The off-grid / on-grid switching control method further includes: When the target relay is not activated and the voltage at the AC load port is greater than a preset voltage value, the voltage parameters of the AC load port and the target energy port are obtained; If the voltage parameters of the AC load port and the target energy port are consistent, then the target relay fault signal is output.

9. A power converter, characterized in that, include: Controller, power conversion circuit and AC load port; The DC side of the power conversion circuit is connected to a DC power supply. The AC side of the power conversion circuit is connected to the first energy port and the second energy port, respectively. The first energy port is used to connect to the power grid, the second energy port is used to connect to the standby generator, and the AC load port is used to connect to the AC load. The controller performs the off-grid / on-grid switching control method as described in any one of claims 1-8.

10. The power converter according to claim 9, characterized in that, The DC power source includes at least one of photovoltaic power and battery power.

11. The power converter according to claim 9, characterized in that, The power converter also includes a relay drive circuit, which includes a grid relay drive branch and a generator relay drive branch. The power grid relay drive branch is used to control the first energy port to be turned on or off. The generator relay drive branch is used to control the second energy port to be turned on or off. The drive signal of the power grid relay is connected to the base circuit of the transistor in the generator relay drive branch. When the drive signal is low, the base of the transistor in the generator relay drive branch is pulled low.

12. The power converter according to claim 9 or 11, characterized in that, The power converter also includes a dual-coil mechanical interlock relay; The two sets of coils of the dual-coil mechanical interlock relay are used to control the grid-side contacts and the generator-side contacts respectively. At the same time, only one contact of the grid-side contacts and the generator-side contacts is closed. When the grid side triggers a closure, the first energy port is turned on. When the generator-side contacts are closed, the second energy port is turned on.

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