Grid-connected and off-grid switching control method of power converter, storage medium, product and power converter

Abstract

The invention belongs to the technical field of power electronics, and discloses a grid-connected and off-grid switching control method of a power converter, a storage medium, a product and the power converter. When the power grid is detected to be abnormal, the power grid side relay is controlled to be switched from the closed state to the open state, in the process, the control mode of the power converter is switched from the current source mode to the voltage source mode, and the power converter can be switched from the closed state to the open state for a long time. The control mode of the power converter is switched from a current source mode to a voltage source mode on line, then a power grid side relay is completely in a disconnected state, and all control rings in the current source mode and all control rings in the voltage source mode operate at the same time in the grid-connected operation mode and the off-grid operation mode. Therefore, the control mode of the power converter is switched from the current source mode to the voltage source mode, a control loop does not need to be operated again, smooth switching from grid-connected operation to off-grid operation of the power converter can be achieved, and normal power supply of a load is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronics, and particularly relates to a parallel-off-grid switching control method of a power converter, a storage medium, a product and the power converter. BACKGROUND

[0002] Generally, a load is connected to an off-grid port of a power converter, and a parallel port of the power converter is connected to a power grid. When the power grid is normal, the power converter operates in a parallel grid mode as a current source, and the load is powered by the power converter and the power grid. When the power grid is abnormal, the power converter switches to an off-grid voltage source operation mode to continue to power the load, and meanwhile, a relay on the power grid side is disconnected from the power grid. However, the relay on the power grid side has a long action time, which may cause interruption of power supply to the load. Therefore, how to realize smooth switching of the power converter from the parallel grid to the off-grid operation mode and ensure normal power supply to the load becomes a problem to be solved. SUMMARY

[0003] The main purpose of the present application is to provide a parallel-off-grid switching control method of a power converter, a storage medium, a product and the power converter, and aims to solve the technical problem of how to realize smooth switching of the power converter from the parallel grid to the off-grid operation mode and ensure normal power supply to the load.

[0004] To achieve the above purpose, the present application provides a parallel-off-grid switching control method of a power converter, which comprises the following steps:

[0005] When the operation mode of the power converter is a parallel grid operation mode, if it is detected that the power grid is abnormal, the relay on the power grid side is switched from a closed state to an open state, all control loops in a current source mode and all control loops in a voltage source mode are simultaneously operated in a parallel grid operation mode, and the mode is controlled through the current source mode;

[0006] During the process of switching the relay on the power grid side from the closed state to the open state, the control mode of the power converter is switched from the current source mode to the voltage source mode;

[0007] When the control mode of the power converter is the voltage source mode, if the relay on the power grid side is in the open state, the operation mode of the power converter is switched from the parallel grid operation mode to an off-grid operation mode, all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated in the off-grid operation mode, and the mode is controlled through the voltage source mode.

[0008] Optionally, after the step of switching the control mode of the power converter from the current source mode to the voltage source mode during the process of switching the relay on the power grid side from the closed state to the open state, the parallel-off-grid switching control method of the power converter further comprises:

[0009] In the voltage source mode, the grid voltage is compared with a first preset threshold to obtain a first comparison result;

[0010] The power converter reference signal is determined according to the first comparison result;

[0011] The power converter control voltage is determined according to the power converter reference signal and the actual output signal of the power converter, and the PWM signal pulse width is adjusted according to the power converter control voltage.

[0012] Optionally, the step of determining the power converter reference signal according to the first comparison result specifically includes:

[0013] When the first comparison result is that the grid voltage is higher than or equal to the first preset threshold, the amplitude corresponding to the power converter reference signal is determined as the grid voltage, the frequency corresponding to the power converter reference signal is determined as the grid frequency, and the phase corresponding to the power converter reference voltage is determined as the grid phase.

[0014] Optionally, the step of determining the power converter reference signal according to the first comparison result specifically includes:

[0015] When the first comparison result is that the grid voltage is lower than the first preset threshold, the bus voltage is compared with a second preset threshold to obtain a second comparison result;

[0016] The power converter reference signal is determined according to the second comparison result.

[0017] Optionally, the step of determining the power converter reference signal according to the second comparison result specifically includes:

[0018] When the second comparison result is that the bus voltage is lower than the second preset threshold, the amplitude corresponding to the power converter reference signal is reduced based on a preset voltage to obtain a target amplitude corresponding to the power converter reference signal;

[0019] The frequency corresponding to the power converter reference signal is determined as a preset frequency, and the phase corresponding to the power converter reference voltage is determined as a preset phase.

[0020] Optionally, the step of determining the power converter reference signal according to the second comparison result specifically includes:

[0021] When the second comparison result is that the bus voltage is higher than or equal to the second preset threshold, the amplitude corresponding to the power converter reference signal is increased based on a preset voltage to obtain a target amplitude corresponding to the power converter reference signal;

[0022] The frequency corresponding to the power converter reference signal is determined as a preset frequency, and the phase corresponding to the power converter reference voltage is determined as a preset phase.

[0023] Optionally, the step of determining the power converter control voltage according to the power converter reference signal and the power converter actual output signal, and adjusting the pulse width of the PWM signal according to the power converter control voltage specifically comprises:

[0024] If the grid has a non-island fault, the power converter control voltage is determined according to the reactive power, active power, reference voltage, reference current corresponding to the power converter reference signal, and the power converter actual output signal;

[0025] If the grid has an island fault, the power converter control voltage is determined according to the reference voltage, reference current corresponding to the power converter reference signal, and the power converter actual output signal;

[0026] The pulse width of the PWM signal is adjusted according to the power converter control voltage.

[0027] In addition, to achieve the above-mentioned purpose, the present application also provides a power converter, which comprises: an inverter circuit composed of a plurality of switching tubes, a filtering module, and a control module, the inverter circuit is connected with the control module, a direct current power supply, and the filtering module respectively, and the filtering module is further connected with a load;

[0028] The control module is used for adjusting the pulse width of the PWM signal according to the collected power converter actual output signal, and sending the obtained target PWM signal to the inverter circuit;

[0029] The inverter circuit is used for converting the direct current provided by the direct current power supply into alternating current according to the target PWM signal when receiving the target PWM signal, and sending the alternating current to the filtering module;

[0030] The filtering module is used for filtering the alternating current when receiving the alternating current, and supplying power to the load according to the filtered alternating current.

[0031] In addition, to achieve the above-mentioned purpose, the present application also provides a storage medium, which is a computer readable storage medium, and the storage medium stores a computer program, and the computer program is executed by a processor to realize the steps of the on-grid and off-grid switching control method of the power converter as described above.

[0032] In addition, to achieve the above-mentioned purpose, the present application also provides a computer program product, which comprises a computer program, and the computer program is executed by a processor to realize the steps of the on-grid and off-grid switching control method of the power converter as described above.

[0033] The application controls the grid-side relay to switch from the closed state to the open state when the power converter operating mode is the grid-connected operating mode and the grid abnormality is detected, all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated in the grid-connected operating mode, and the mode controlled by the current source mode, the power converter control mode is switched from the current source mode to the voltage source mode in the process of the grid-side relay switching from the closed state to the open state, the power converter operating mode is switched from the grid-connected operating mode to the off-grid operating mode when the power converter control mode is the voltage source mode and the grid-side relay is in the open state, all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated in the off-grid operating mode, and the mode controlled by the voltage source mode. When the grid abnormality is detected, the application controls the grid-side relay to switch from the closed state to the open state, and in the process, the power converter control mode is switched from the current source mode to the voltage source mode. The power converter control mode can be switched from the current source mode to the voltage source mode online for a long time when the grid-side relay switches from the closed state to the open state, and then the grid-side relay is completely in the open state. Since all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated in the grid-connected operating mode and the off-grid operating mode, the power converter control mode is switched from the current source mode to the voltage source mode, which can realize smooth switching of the power converter from the grid-connected to the off-grid operating mode and ensure normal power supply of the load. BRIEF DESCRIPTION OF DRAWINGS

[0034] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0036] Figure 1 Flowchart of an embodiment of the grid-connected and off-grid switching control method of the power converter of the present application;

[0037] Figure 2 Power system diagram of an embodiment of the grid-connected and off-grid switching control method of the power converter of the present application;

[0038] Figure 3 Power converter control diagram of an embodiment of the grid-connected and off-grid switching control method of the power converter of the present application;

[0039] Figure 4Flowchart of an embodiment of the parallel off-grid switching control method of the power converter of the present application;

[0040] Figure 5 Voltage regulation control diagram of an embodiment of the parallel off-grid switching control method of the power converter of the present application;

[0041] Figure 6 System principle block diagram of the power converter of the present application.

[0042] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0043] It should be understood that the specific embodiments described herein are merely intended to explain the technical solutions of the present application, and are not intended to limit the present application.

[0044] In order to better understand the technical solutions of the present application, the specific embodiments will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] It should be noted that the execution subject of the present application can be a microcontroller unit (MCU) in the power converter, and the present application is applicable to power converters, such as inverters, rectifiers, frequency converters, etc.

[0046] Based on this, the present application provides a parallel off-grid switching control method of a power converter, which will be described below with reference to the accompanying drawings. Figure 1 , Figure 1 Flowchart of an embodiment of the parallel off-grid switching control method of the power converter of the present application.

[0047] In this embodiment, the parallel off-grid switching control method of the power converter comprises the following steps:

[0048] Step S10: When the power converter is in a grid-connected operation mode, if an abnormality of the power grid is detected, the grid-side relay is switched from a closed state to an open state, all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated, and the mode controlled by the current source mode is operated.

[0049] It should be understood that the parallel off-grid switching control method of the power converter of the present application is applicable to various power converters, such as inverters, rectifiers, frequency converters, etc. Figure 2 , Figure 2 Power system diagram of an embodiment of the parallel off-grid switching control method of the power converter of the present application, as shown in Figure 2 For example, the power converter is an inverter, which not only can generate electricity in parallel with the power grid, but also has the ability to independently run with load in the event of abnormality of the power grid, Figure 2The load in the power converter is connected to the off-grid port of the power converter, and the power converter grid port is connected to the power grid. When the power grid is normal, the power converter operates in the current source grid-connected mode, and the load is powered by the power converter and the power grid; when the power grid is abnormal, the power converter switches to the off-grid voltage source operation mode to continue to power the load, and the power grid side relay is disconnected from the power grid.

[0050] It should be understood that when the power converter operating mode is the grid-connected operation mode, the power converter can detect the power grid information in real time, and when the power grid has an abnormality, such as islanding, over frequency, under frequency, over voltage, under voltage, etc., a tripping instruction can be sent to the power grid side relay, i.e. controlling the power grid side relay to switch from the closed state to the open state. The grid-connected operation mode in this embodiment can be a mode in which all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated, and the control is performed through the current source mode. At this time, all control loops in the voltage source mode are still in the running state, but the power converter is not controlled through the voltage source mode. The control loops can include power loops, voltage loops, current loops, etc.

[0051] Step S20: During the process of switching the power grid side relay from the closed state to the open state, the power converter control mode is switched from the current source mode to the voltage source mode.

[0052] It can be understood that during the process of switching the power grid side relay from the closed state to the open state, since this process may require a long time, the power converter control mode can be switched from the current source mode to the voltage source mode online during this process.

[0053] It should be understood that referring to Figure 3 , Figure 3 is a power converter control diagram of an embodiment of the power converter of the power converter grid-connected and off-grid switching control method of the present application. As Figure 3 shown, the switching of the power converter control mode can be realized by the MCU, i.e. from the current source mode to the voltage source mode. Specifically, the weighting coefficient of the control loop corresponding to the current source mode can be adjusted, i.e. K is reduced. At this time, the weighting coefficient of the control loop corresponding to the voltage source mode will also be adjusted accordingly, i.e. 1-K is increased. After adjusting the weighting coefficient, the power converter control mode can be switched from the current source mode to the voltage source mode.

[0054] Step S30: When the power converter control mode is the voltage source mode, if the power grid side relay is in the open state, the power converter operating mode is switched from the grid-connected operation mode to the off-grid operation mode. The off-grid operation mode is a mode in which all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated, and the control is performed through the voltage source mode.

[0055] It can be understood that, after the power converter control mode is switched to the voltage source control mode, if the grid side relay is in the open state, it indicates that the power converter operating mode is switched from the grid-connected operating mode to the off-grid operating mode. The off-grid operating mode in the embodiment can be a mode in which all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated and controlled through the voltage source mode. Therefore, during the switching from the grid-connected operating mode to the off-grid operating mode, since all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated, only the power converter control mode needs to be switched from the current source mode to the voltage source mode, and all control loops in the voltage source mode do not need to be switched from the stop state to the operating state again, so that the smooth switching of the power converter from the grid-connected to the off-grid operating mode can be realized, and the switching time is reduced.

[0056] In the embodiment, when the power converter operating mode is the grid-connected operating mode, if the grid abnormality is detected, the grid side relay is controlled to be switched from the closed state to the open state, the grid-connected operating mode is a mode in which all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated and controlled through the current source mode, during the switching of the grid side relay from the closed state to the open state, the power converter control mode is switched from the current source mode to the voltage source mode, and when the power converter control mode is the voltage source mode, if the grid side relay is in the open state, the power converter operating mode is switched from the grid-connected operating mode to the off-grid operating mode, and the off-grid operating mode is a mode in which all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated and controlled through the voltage source mode. In the embodiment, when the grid abnormality is detected, the grid side relay is controlled to be switched from the closed state to the open state, during the switching, the power converter control mode is switched from the current source mode to the voltage source mode, and the power converter control mode is online switched from the current source mode to the voltage source mode in a relatively long time during which the grid side relay is switched from the closed state to the open state, and then the grid side relay is kept in the open state. Since all control loops in the current source mode and all control loops in the voltage source mode are simultaneously operated in the grid-connected operating mode and the off-grid operating mode, the power converter control mode is switched from the current source mode to the voltage source mode without re-operating the control loops, so that the smooth switching of the power converter from the grid-connected to the off-grid operating mode can be realized, and the normal power supply of the load is ensured.

[0057] Reference Figure 4 , Figure 4 FIG. 1 is a flowchart of an embodiment of the power converter grid-connected and off-grid switching control method.

[0058] After step S20, the method further includes:

[0059] Step S201: When the power converter control mode is voltage source mode, the grid voltage is compared with the first preset threshold to obtain the first comparison result.

[0060] Understandably, the islanded voltage will continue to drop, while the undervoltage drop will only be partial, both initially following the grid voltage source control. When an islanding fault occurs in the grid, detection takes some time, but the voltage will continue to drop. Before an islanding fault is detected, the voltage source maintains voltage control based on the phase-locked loop output voltage. When the grid voltage drops to a first preset threshold, tracking stops.

[0061] It should be understood that, referring to Figure 5 , Figure 5 This is a voltage regulation control diagram of an embodiment of the grid-connected / off-grid switching control method for the power converter of this application, as shown below. Figure 5 As shown, when the power converter control mode is voltage source mode, the grid voltage can be compared with the first preset threshold Umin to obtain the first comparison result. The grid voltage refers to the voltage of the grid connected to the power converter.

[0062] Step S202: Determine the power converter reference signal based on the first comparison result.

[0063] Understandably, before the grid-side relay disconnects, there may be other loads in the grid. In this case, voltage regulation is applied to prevent the power converter from shutting down due to overload. Specifically, the power converter reference signal can be determined based on the first comparison result, and then the amplitude, frequency, and phase of the power converter reference signal can be determined.

[0064] Furthermore, in order to accurately determine the power converter reference signal, in this embodiment, step S202 includes: when the first comparison result is that the grid voltage is higher than or equal to a first preset threshold, determining that the amplitude of the power converter reference signal is the grid voltage, the frequency of the power converter reference signal is the grid frequency, and the phase of the power converter reference voltage is the grid phase.

[0065] It should be understood that when the first comparison result is that the grid voltage is higher than or equal to the first preset threshold, it indicates that the grid voltage is sufficient to supply power to the internal and external loads of the power converter. The grid may have an undervoltage fault. At this time, the power converter is controlled synchronously with the grid. That is, the amplitude Uref corresponding to the power converter reference signal is the grid voltage Ugrid, the frequency Wref corresponding to the power converter reference signal is the grid frequency Wgrid, and the phase ThetaRef corresponding to the power converter reference voltage is the grid phase ThetaGrid.

[0066] Further, in the embodiment, the step S202 further comprises: comparing the bus voltage with a second preset threshold Vdcmin to obtain a second comparison result when the first comparison result is that the grid voltage is lower than the first preset threshold Umin; and determining the power converter reference signal according to the second comparison result.

[0067] It can be understood that when the first comparison result is that the grid voltage is lower than the first preset threshold Umin, it is determined that the grid is out of power, i.e., an islanding fault occurs, and the power converter needs to be used as a power supply to supply power to the load. At this time, the bus voltage can be compared with the second preset threshold Vdcmin to obtain a second comparison result, the bus voltage can be the voltage across the capacitor connected in parallel with the DC source, and the power converter reference signal is determined according to the second comparison result, and then the amplitude, frequency and phase corresponding to the power converter reference signal are determined.

[0068] Further, in the embodiment, the step of determining the power converter reference signal according to the second comparison result specifically comprises: reducing the amplitude corresponding to the power converter reference signal based on a preset voltage to obtain a target amplitude corresponding to the power converter reference signal when the second comparison result is that the bus voltage is lower than the second preset threshold Vdcmin; determining that the frequency corresponding to the power converter reference signal is a preset frequency, and the phase corresponding to the power converter reference voltage is a preset phase.

[0069] It should be understood that when the second comparison result is that the bus voltage is lower than the second preset threshold, it indicates that the bus voltage is insufficient to supply power to the load, and at this time, the amplitude corresponding to the power converter reference signal should be gradually reduced, i.e., the output voltage of the power converter is gradually reduced. Specifically, the amplitude corresponding to the power converter reference signal can be reduced based on a preset voltage to obtain a target amplitude, i.e., the target amplitude Uref+=ΔU, ΔU is the preset voltage. The frequency and phase corresponding to the power converter reference signal are not specifically limited, for example, the frequency Wref corresponding to the power converter reference signal is a preset frequency Wrate, and the phase ThetaRef corresponding to the power converter reference voltage is a preset phase Thetarate.

[0070] Further, in the embodiment, the step of determining the power converter reference signal according to the second comparison result specifically comprises: increasing the amplitude corresponding to the power converter reference signal based on a preset voltage to obtain a target amplitude corresponding to the power converter reference signal when the second comparison result is that the bus voltage is higher than or equal to the second preset threshold; and determining that the frequency corresponding to the power converter reference signal is a preset frequency, and the phase corresponding to the power converter reference voltage is a preset phase.

[0071] In a specific implementation, when the second comparison result is that the bus voltage is higher than or equal to the second preset threshold, it indicates that the bus voltage is sufficient to power the load, at this time, the amplitude corresponding to the power converter reference signal should be gradually increased, that is, the power converter output voltage is gradually increased, and specifically, the amplitude corresponding to the power converter reference signal can be increased based on a preset voltage to obtain a target amplitude, that is, the target amplitude Uref- = ΔU, ΔU is the preset voltage, and the frequency and phase corresponding to the power converter reference signal are not specifically limited, for example, the frequency Wref corresponding to the power converter reference signal is a preset frequency Wrate, and the phase ThetaRef corresponding to the power converter reference voltage is a preset phase Thetarate.

[0072] Step S203: determining a power converter control voltage according to the power converter reference signal and the power converter actual output signal, and adjusting the PWM signal pulse width according to the power converter control voltage.

[0073] It can be understood that, based on the power converter reference signal, the reference reactive power Qset, the reference active power Pset, the reference d-axis voltage Vdref, the reference q-axis voltage Vqref, the reference d-axis current Idref, and the reference q-axis current Iqref in the following formula can be obtained. Figure 3 The power converter actual output signal refers to the currently sampled output signal of the power converter, and can include the actual reactive power Qe, the actual active power Pe, the actual angular velocity Wn, the actual output current Iabc, the actual output voltage Uabc, the converted actual d-axis voltage Vd, the actual q-axis voltage Vq, the actual d-axis current Id, and the actual q-axis current Iq.

[0074] In a specific implementation, after switching to the voltage source mode, the voltage source in the blue part works, the value of Qset-Qe is subjected to 1 / n droop control to obtain a voltage value +Vdref, the obtained voltage value -Vd is subjected to PI adjustment to obtain a current value -Id, and the obtained current value is subjected to PI adjustment to obtain a voltage value, and the voltage value is subjected to a weighting coefficient 1-K to obtain Ud, that is, the d-axis control voltage. Similarly, Uq, that is, the q-axis control voltage, can be obtained. Then, Ud and Uq are converted into a three-phase control voltage Uabc, so as to adjust the PWM signal pulse width according to Uabc.

[0075] Further, in the embodiment, step S203 includes: if the power grid has a non-island fault, determining the power converter control voltage according to the reactive power, the active power, the reference voltage, the reference current corresponding to the power converter reference signal, and the power converter actual output signal; if the power grid has an island fault, determining the power converter control voltage according to the reference voltage, the reference current corresponding to the power converter reference signal, and the power converter actual output signal; and adjusting the PWM signal pulse width according to the power converter control voltage.

[0076] It can be understood that if the power grid has a non-island fault, for example, frequency jitter, over / under voltage, over / under frequency, etc., at this time, the power outer loop control, i.e., the power loop of Qset-Qe and the power loop of Pset-Pe, is effective, at this time, the power converter control voltage can be determined according to the corresponding reactive power Qset, active power Pset, reference voltage Vdref and Vqref, reference current Idref and Iqref of the power converter reference signal, and the actual output signal of the power converter, which can include actual reactive power Qe, actual active power Pe, actual angular velocity Wn, actual output current Iabc, actual output voltage Uabc, converted actual d-axis voltage Vd, actual q-axis voltage Vq, actual d-axis current Id, and actual q-axis current Iq.

[0077] It should be understood that if the power grid has an island fault, at this time, the power outer loop is invalid, i.e., the power loop of Qset-Qe and the power loop of Pset-Pe are invalid, at this time, the power converter control voltage can be determined according to the corresponding reference voltage Vdref and Vqref, reference current Idref and Iqref of the power converter reference signal, and the actual output signal of the power converter, which can include actual angular velocity Wn, actual output current Iabc, actual output voltage Uabc, converted actual d-axis voltage Vd, actual q-axis voltage Vq, actual d-axis current Id, and actual q-axis current Iq.

[0078] The embodiment compares the grid voltage with the first preset threshold when the power converter control mode is the voltage source mode, obtains a first comparison result, then determines the power converter reference signal according to the first comparison result, determines the power converter control voltage according to the power converter reference signal and the actual output signal of the power converter, and adjusts the PWM signal pulse width according to the power converter control voltage. The embodiment compares the grid voltage with the first preset threshold when the power converter control mode is the voltage source mode, can determine whether the grid voltage can supply power to the load, then determines the power converter reference signal according to the first comparison result, effectively determines the power converter control voltage according to the power converter reference signal and the actual output signal of the power converter, and prevents the power converter from shutting down due to overloading.

[0079] Referring to Figure 6 , Figure 6 The system principle block diagram of the power converter of the present application is shown in the figure.

[0080] As Figure 6 shown, the power converter proposed in the embodiment of the present application comprises an inverter circuit composed of a plurality of switching tubes, a filtering module, and a control module, the inverter circuit is connected with the control module, a direct current power supply, and the filtering module respectively, and the filtering module is further connected with a load.

[0081] a control module configured to adjust a pulse width of the PWM signal according to the actual output signal of the power converter, and transmit a target PWM signal to the inverter circuit;

[0082] It can be understood that the control module in the embodiment can be a microcontroller unit (MCU), which can implement the off-grid switching control method of the power converter. The control module can adjust the pulse width of the PWM signal according to the actual output signal of the power converter, obtain a target PWM signal, and transmit the target PWM signal to the switch tube.

[0083] Further, in the embodiment, the control module is further configured to compare the grid voltage with a first preset threshold when the power converter control mode is the voltage source mode, and obtain a first comparison result.

[0084] It should be understood that the island voltage will continue to drop, and the under-voltage will only drop a part, both of which will first follow the grid for voltage source control. When the grid occurs island fault, detection needs a certain time, but the voltage will continue to drop. When the island fault is not detected, the voltage source remains to perform voltage source control with the voltage output by the phase-locked loop, and stops tracking when the grid voltage drops to the first preset threshold. When the power converter control mode is the voltage source mode, the grid voltage can be compared with the first preset threshold Umin to obtain the first comparison result.

[0085] The control module is further configured to determine a power converter reference signal according to the first comparison result.

[0086] It can be understood that before the grid-side relay is disconnected, there can be other loads in the grid, at which time voltage regulation is added to prevent the power converter from shutting down due to overload. Specifically, the power converter reference signal can be determined according to the first comparison result, and then the amplitude, frequency, and phase corresponding to the power converter reference signal can be determined.

[0087] Further, in the embodiment, the control module is further configured to determine that the amplitude corresponding to the power converter reference signal is the grid voltage, the frequency corresponding to the power converter reference signal is the grid frequency, and the phase corresponding to the power converter reference voltage is the grid phase when the first comparison result is that the grid voltage is higher than or equal to the first preset threshold.

[0088] It should be understood that when the first comparison result is that the grid voltage is higher than or equal to the first preset threshold, it indicates that the grid voltage is sufficient to supply power to the internal load and the external load of the power converter, and the grid may have an under-voltage fault, and at this time, the power converter is controlled synchronously with the grid, that is, the amplitude Uref of the power converter reference signal corresponds to the grid voltage Ugrid, the frequency Wref of the power converter reference signal corresponds to the grid frequency Wgrid, and the phase ThetaRef of the power converter reference voltage corresponds to the grid phase ThetaGrid.

[0089] The control module is also configured to determine a power converter control voltage according to the power converter reference signal and the power converter actual output signal, and adjust the pulse width of the PWM signal according to the power converter control voltage.

[0090] It can be understood that the reference reactive power Qset, the reference active power Pset, the reference d-axis voltage Vdref, the reference q-axis voltage Vqref, the reference d-axis current Idref, and the reference q-axis current Iqref in the power converter reference signal can be obtained based on the power converter reference signal. Figure 2 The power converter actual output signal refers to the output signal of the power converter sampled at the current moment, and can include the actual reactive power Qe, the actual active power Pe, the actual angular velocity Wn, the actual output current Iabc, the actual output voltage Uabc, the converted actual d-axis voltage Vd, the actual q-axis voltage Vq, the actual d-axis current Id, and the actual q-axis current Iq.

[0091] In a specific implementation, after switching to the voltage source mode, the voltage source in the blue part works, the value of Qset-Qe is subjected to 1 / n droop control to obtain a voltage value +Vdref, the voltage value -Vd is obtained, the current value -Id is obtained through PI adjustment, the voltage value is obtained through PI adjustment, the weighting coefficient 1-K is used to obtain Ud, that is, the d-axis control voltage. Similarly, Uq, that is, the q-axis control voltage, can be obtained. Then, Ud and Uq are converted into three-phase control voltage Uabc, so as to adjust the pulse width of the PWM signal according to Uabc.

[0092] The inverter circuit is configured to convert the direct current provided by the direct current power supply into alternating current according to the target PWM signal when the target PWM signal is received, and send the alternating current to the filtering module.

[0093] It should be understood that the inverter circuit in the embodiment refers to a circuit for converting direct current into alternating current, and can also be an inverter bridge, which can be composed of a plurality of switching tubes, and the switching tubes can be IGBT or MOS tubes. When the target PWM signal is received, the inverter circuit converts the direct current input by the PV direct current source into alternating current according to the target PWM signal.

[0094] The filtering module is used to filter the AC power received and then supply power to the load based on the filtered AC power.

[0095] In a specific implementation, the filtering module in this embodiment can be an LCL filtering module, which can filter the AC power when it is received and supply power to the load based on the filtered AC power.

[0096] In this embodiment, the control module adjusts the PWM signal pulse width according to the actual output signal of the power converter to obtain the target PWM signal. Then, the switching transistor converts the input DC power into AC power according to the target PWM signal. The filtering module then filters the AC power and supplies power to the load using the filtered AC power. This embodiment first adjusts the PWM signal pulse width according to the actual output signal of the power converter through the control module, enabling real-time and effective acquisition of the target PWM signal. Then, the switching transistor converts the input DC power into AC power according to the target PWM signal, thereby effectively supplying power to the load.

[0097] This application provides a computer-readable storage medium having computer-readable program instructions (i.e., a computer program) stored thereon, the computer-readable program instructions being used to execute the grid-connected / off-grid switching control method for the power converter in the above embodiments.

[0098] The computer-readable storage medium provided in this application may be, for example, a USB flash drive, but is not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or any combination thereof. More specific examples of computer-readable storage media may include, but are not limited to: electrical connections having one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, system, or device. The program code contained on the computer-readable storage medium may be transmitted using any suitable medium, including but not limited to: wires, optical cables, RF (Radio Frequency), etc., or any suitable combination thereof.

[0099] Computer program code for performing the operations of this application can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a Local Area Network (LAN) or a Wide Area Network (WAN)—or can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0100] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0101] The modules described in the embodiments of this application can be implemented in software or hardware. The names of the modules do not necessarily limit the functionality of the unit itself.

[0102] The readable storage medium provided in this application is a computer-readable storage medium that stores computer-readable program instructions (i.e., a computer program) for executing the above-described power converter grid-connected / off-grid switching control method. This solves the technical problem of how to achieve a smooth switching of the power converter from grid-connected to off-grid operation and ensure normal power supply to the load. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided in this application are the same as those of the power converter grid-connected / off-grid switching control method provided in the above embodiments, and will not be repeated here.

[0103] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the above-described power converter grid-to-offline switching control method.

[0104] The computer program product provided in this application can solve the technical problem of how to achieve a smooth switching of power converter from grid-connected to off-grid operation and ensure normal power supply to the load. Compared with the prior art, the beneficial effects of the computer program product provided in this application are the same as the beneficial effects of the grid-connected / off-grid switching control method for power converters provided in the above embodiments, and will not be repeated here.

[0105] The above are only some embodiments of this application and do not limit the patent scope of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. A method for controlling the grid-connected / off-grid switching of a power converter, characterized in that, The grid-connected / off-grid switching control method for the power converter includes the following steps: When the power converter is in grid-connected operation mode, if a grid abnormality is detected, the grid-side relay is controlled to switch from the closed state to the open state. The grid-connected operation mode is a mode in which all control loops in the current source mode and all control loops in the voltage source mode operate simultaneously, and are controlled through the current source mode. During the process of the grid-side relay switching from the closed state to the open state, the power converter control mode is switched from the current source mode to the voltage source mode; When the power converter control mode is the voltage source mode, if the grid-side relay is in the open state, the power converter operation mode is switched from the grid-connected operation mode to the off-grid operation mode. The off-grid operation mode is a mode in which all control loops in the current source mode and all control loops in the voltage source mode operate simultaneously and are controlled by the voltage source mode.

2. The grid-connected / off-grid switching control method for a power converter as described in claim 1, characterized in that, After the step of switching the power converter control mode from the current source mode to the voltage source mode during the process of the grid-side relay switching from the closed state to the open state, the method further includes: When the power converter control mode is the voltage source mode, the grid voltage is compared with a first preset threshold to obtain a first comparison result; The power converter reference signal is determined based on the first comparison result; The power converter control voltage is determined based on the power converter reference signal and the actual output signal of the power converter, and the PWM signal pulse width is adjusted based on the power converter control voltage.

3. The grid-connected / off-grid switching control method for a power converter as described in claim 2, characterized in that, The step of determining the power converter reference signal based on the first comparison result specifically includes: When the first comparison result indicates that the grid voltage is higher than or equal to the first preset threshold, the amplitude of the power converter reference signal is determined to be the grid voltage, the frequency of the power converter reference signal is the grid frequency, and the phase of the power converter reference voltage is the grid phase.

4. The grid-connected / off-grid switching control method for a power converter as described in claim 2, characterized in that, The step of determining the power converter reference signal based on the first comparison result specifically includes: When the first comparison result indicates that the grid voltage is lower than the first preset threshold, the bus voltage is compared with the second preset threshold to obtain a second comparison result; The power converter reference signal is determined based on the second comparison result.

5. The grid-connected / off-grid switching control method for a power converter as described in claim 4, characterized in that, The step of determining the power converter reference signal based on the second comparison result specifically includes: When the second comparison result indicates that the bus voltage is lower than the second preset threshold, the amplitude of the power converter reference signal is reduced based on the preset voltage to obtain the target amplitude of the power converter reference signal. The frequency corresponding to the power converter reference signal is determined to be a preset frequency, and the phase corresponding to the power converter reference voltage is determined to be a preset phase.

6. The grid-connected / off-grid switching control method for a power converter as described in claim 4, characterized in that, The step of determining the power converter reference signal based on the second comparison result specifically includes: When the second comparison result indicates that the bus voltage is higher than or equal to the second preset threshold, the amplitude of the power converter reference signal is increased based on the preset voltage to obtain the target amplitude of the power converter reference signal. The frequency corresponding to the power converter reference signal is determined to be a preset frequency, and the phase corresponding to the power converter reference voltage is determined to be a preset phase.

7. The grid-connected / off-grid switching control method for a power converter as described in claim 2, characterized in that, The step of determining the power converter control voltage based on the power converter reference signal and the actual output signal of the power converter, and adjusting the PWM signal pulse width based on the power converter control voltage, specifically includes: If a non-islanding fault occurs in the power grid, the power converter control voltage is determined based on the reactive power, active power, reference voltage, reference current, and the actual output signal of the power converter corresponding to the power converter reference signal. If an islanding fault occurs in the power grid, the power converter control voltage is determined based on the reference voltage and reference current corresponding to the power converter reference signal and the actual output signal of the power converter. The PWM signal pulse width is adjusted according to the control voltage of the power converter.

8. A power converter, characterized in that, The power converter includes: an inverter circuit composed of multiple switching transistors, a filter module, and a control module. The inverter circuit is connected to the control module, a DC power supply, and the filter module. The filter module is also connected to the load. The control module is used to adjust the PWM signal pulse width according to the actual output signal of the power converter, and send the obtained target PWM signal to the inverter circuit. The inverter circuit is used to convert the DC power supplied by the DC power supply into AC power according to the target PWM signal when the target PWM signal is received, and send the AC power to the filter module. The filtering module is used to filter the AC power when it is received, and to supply power to the load based on the filtered AC power.

9. The power converter as described in claim 8, characterized in that, The control module is also used to compare the grid voltage with a first preset threshold and obtain a first comparison result when the power converter control mode is voltage source mode; The control module is further configured to determine a power converter reference signal based on the first comparison result; The control module is further configured to determine the power converter control voltage based on the power converter reference signal and the power converter actual output signal, and adjust the PWM signal pulse width based on the power converter control voltage.

10. The power converter as claimed in claim 8, characterized in that, The control module is further configured to determine, when the first comparison result is that the grid voltage is higher than or equal to the first preset threshold, that the amplitude corresponding to the power converter reference signal is the grid voltage, the frequency corresponding to the power converter reference signal is the grid frequency, and the phase corresponding to the power converter reference voltage is the grid phase.

11. A storage medium, characterized in that, The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, it implements the steps of the power converter grid-to-off-grid switching control method as described in any one of claims 1 to 7.

12. A computer program product, characterized in that, The computer program product includes a computer program that, when executed by a processor, implements the steps of the grid-connected / off-grid switching control method for the power converter as described in any one of claims 1 to 7.

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