Power grid voltage drop detection method and related equipment

Abstract

The invention provides a power grid voltage drop detection method and related equipment. The detection method can be applied to a photovoltaic inverter in a grid-connected state, and comprises the steps that the voltage of an alternating-current power grid is collected according to a preset frequency, sampling voltage is obtained, and the alternating-current power grid is connected with the alternating-current side of the photovoltaic inverter; determining a modulation wave of the photovoltaic inverter based on the phase of the sampling voltage; and determining whether the voltage of the AC power grid drops based on the sampling voltage and the modulation wave. The technical scheme provided by the invention can improve the accuracy of detecting whether the voltage of the alternating-current power grid drops or not.

Description

Technical Field

[0001] This invention relates to the field of new energy technology, and in particular to a method and related equipment for detecting grid voltage dips. Background Technology

[0002] In a photovoltaic power station, a photovoltaic inverter can receive direct current (DC) from photovoltaic modules on the DC side, convert the DC to alternating current (AC), and output the AC voltage to the AC grid on the AC side, thereby supplying power to AC loads.

[0003] To ensure grid connection safety and power quality of photovoltaic inverters, photovoltaic inverters often use a phase-locked loop (PLL) to lock the grid voltage and calculate the modulation wave based on the phase angle. The modulation wave is then used to generate a pulse-width modulation (PWM) signal, which is used to adjust the duty cycle of the AC voltage output by the photovoltaic inverter to achieve synchronization between the AC voltage and the AC grid.

[0004] However, when a grid voltage drop occurs due to a fault, the phase-locked loop (PLL) responds more slowly than the grid voltage drop, causing the modulation wave to fail to track the sudden change in grid voltage in time. This can lead to a severe operating condition where the grid voltage and the modulation wave are not in the same half-cycle, resulting in a desynchronization between the AC voltage output of the photovoltaic inverter and the AC grid. This can trigger a large current surge, damaging the power modules (such as insulated-gate bipolar transistors, IGBTs) in the photovoltaic inverter. Therefore, detecting grid voltage drops has become a technical challenge. Summary of the Invention

[0005] This application provides a method and related equipment for detecting grid voltage dips, so as to accurately detect grid voltage dips.

[0006] In a first aspect, this application provides a method for detecting grid voltage dips, which can be applied to a photovoltaic inverter in a grid-connected state. The method includes: collecting the voltage of the AC grid at a preset frequency to obtain a sampled voltage, wherein the AC grid is connected to the AC side of the photovoltaic inverter; determining the modulation wave of the photovoltaic inverter based on the phase of the sampled voltage; and determining whether a voltage dip has occurred in the AC grid based on the sampled voltage and the modulation wave.

[0007] In conjunction with the first aspect, in one possible implementation, determining whether the voltage of the AC power grid has dropped based on the sampled voltage and the modulation wave includes: detecting whether the sampled voltage and the modulation wave are in the same half-cycle; if the sampled voltage and the modulation wave are in the same half-cycle, then determining that the AC power grid is in normal operation; if the sampled voltage and the modulation wave are not in the same half-cycle, then determining that the voltage of the AC power grid has dropped.

[0008] In conjunction with the first aspect, in one possible implementation, the method further includes: determining whether the absolute value of the sampled voltage is greater than or equal to the absolute value of a protection threshold; if the sampled voltage and the modulation wave are not in the same half-cycle, and the absolute value of the sampled voltage is greater than or equal to the absolute value of the protection threshold, then the voltage of the AC power grid has dropped.

[0009] In conjunction with the first aspect, in one possible implementation, the sign of the protection threshold is opposite to the sign of the half-cycle in which the modulation wave is located, and the absolute value of the protection threshold is greater than 0.

[0010] In conjunction with the first aspect, in one possible implementation, the protection threshold is also related to the maximum current capability of the power module in the photovoltaic inverter.

[0011] In conjunction with the first aspect, in one possible implementation, the method further includes: using the phase-locked loop of the photovoltaic inverter to lock the sampled voltage in phase to determine the phase of the sampled voltage.

[0012] In conjunction with the first aspect, in one possible implementation, the method further includes: executing a voltage drop protection strategy for the AC power grid when a voltage drop occurs.

[0013] Secondly, this application provides a power grid voltage drop detection device, which includes various modules for implementing the detection method in the first aspect or any of the implementations of the first aspect, and each module can be implemented in hardware and / or software.

[0014] For example, the device may include a processing module. The processing module is configured to acquire the voltage of the AC power grid at a preset frequency to obtain a sampled voltage, wherein the AC power grid is connected to the AC side of the photovoltaic inverter; the processing module is further configured to determine the modulation wave of the photovoltaic inverter based on the phase of the sampled voltage; the processing module is further configured to determine whether a voltage drop has occurred in the AC power grid based on the sampled voltage and the modulation wave.

[0015] In conjunction with the second aspect, in one possible implementation, the processing module is further configured to detect whether the sampled voltage and the modulation wave are in the same half-cycle; if the sampled voltage and the modulation wave are in the same half-cycle, it is determined that the AC power grid is in normal operation; if the sampled voltage and the modulation wave are not in the same half-cycle, it is determined that the voltage of the AC power grid has dropped.

[0016] In conjunction with the second aspect, in one possible implementation, the processing module is further configured to determine whether the absolute value of the sampled voltage is greater than or equal to the absolute value of the protection threshold; if the sampled voltage and the modulation wave are not in the same half-cycle, and the absolute value of the sampled voltage is greater than or equal to the absolute value of the protection threshold, then the voltage of the AC power grid has dropped.

[0017] In conjunction with the second aspect, in one possible implementation, the sign of the protection threshold is opposite to the sign of the half-cycle in which the modulation wave is located, and the absolute value of the protection threshold is greater than 0.

[0018] In conjunction with the second aspect, in one possible implementation, the protection threshold is also related to the maximum current capability of the power module in the photovoltaic inverter.

[0019] In conjunction with the second aspect, in one possible implementation, the processing module is further configured to lock the sampled voltage through the phase-locked loop of the photovoltaic inverter to determine the phase of the sampled voltage.

[0020] In conjunction with the second aspect, in one possible implementation, the processing module is further configured to execute a voltage drop protection strategy for the AC power grid when a voltage drop occurs.

[0021] Thirdly, this application provides a power grid voltage drop detection device, including a processor coupled to a memory, which can be used to execute instructions in the memory to implement the detection method in the first aspect or any possible implementation of the first aspect. Optionally, the device further includes a memory. Optionally, the device further includes a communication interface, and the processor is coupled to the communication interface.

[0022] Fourthly, this application provides a photovoltaic inverter that may include a detection device as described in the second aspect or any possible implementation thereof, or may include a detection device as described in the third aspect or any possible implementation thereof.

[0023] Fifthly, this application provides a computer-readable medium storing program code for execution by a device, the program code including a detection method as described in the first aspect or any possible implementation thereof.

[0024] Sixthly, this application provides a computer program product containing instructions that, when run on a computer, cause the computer to perform the detection method as described in the first aspect or any possible implementation thereof.

[0025] This application provides a method and related equipment for detecting grid voltage dips in photovoltaic inverters. Based on the characteristic that the grid voltage and modulation wave are in the same positive or negative half-cycle under normal grid-connected conditions, but will not be in the same half-cycle when the grid voltage dips due to a fault, this application obtains a sampled voltage by high-frequency acquisition of the AC grid voltage, performs phase-locking on the sampled voltage to obtain the modulation wave, and determines whether a voltage dip has occurred in the AC grid by detecting the sampled voltage and the modulation wave, thereby protecting the photovoltaic inverter. The technical solution provided in this application also sets a protection threshold; a voltage dip is only determined when the absolute value of the sampled voltage exceeds the absolute value of the protection threshold, and a voltage dip protection strategy is executed, improving the accuracy of detection. The technical solution provided in this application can distinguish between dynamic changes in the grid and high / low voltage ride-through events, thereby improving the accuracy of determining whether a voltage dip has occurred in the AC grid and achieving effective protection of the photovoltaic inverter, extending the service life of the power modules in the photovoltaic inverter. The technical solution provided in this application can quickly and accurately detect whether the voltage of the AC power grid has dropped during the dynamic response of the phase-locked loop, without the need for additional components, thus reducing the difficulty and cost of implementation. Attached Figure Description

[0026] Figure 1 A schematic topology diagram of a single-phase capacitive load switching in a photovoltaic power plant, as provided in this application; Figure 2 A schematic flowchart illustrating a method for detecting grid voltage dips provided in this application. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In a photovoltaic power station, a photovoltaic inverter can receive direct current (DC) from photovoltaic modules on the DC side, convert the DC to AC, and then output the AC voltage to the AC grid on the AC side to supply power to AC loads.

[0029] To ensure grid connection safety and power quality of photovoltaic inverters, photovoltaic inverters often use a phase-locked loop (PLL) to lock the grid voltage and calculate the modulation wave based on the phase angle. The modulation wave is then used to generate a pulse-width modulation (PWM) signal. The PWM signal is used to adjust the duty cycle of the AC voltage output by the photovoltaic inverter to synchronize the AC voltage output by the photovoltaic inverter with the AC grid.

[0030] However, if the grid voltage drops due to grid faults or load switching when the photovoltaic inverter is in grid-connected mode, the phase-locked loop (PLL) response time is slower than the grid voltage drop, causing the modulation wave to fail to track the sudden change in grid voltage in time. This can lead to a severe operating condition where the grid voltage and the modulation wave are not in the same half-cycle, resulting in asynchrony between the AC voltage output of the photovoltaic inverter and the grid voltage. When the AC voltage output of the photovoltaic inverter is out of sync with the grid voltage, it can trigger a large current surge, potentially damaging the power modules (such as insulated-gate bipolar transistor (IGBT) modules) in the photovoltaic inverter. Therefore, detecting grid voltage drops becomes a technical problem. It should be noted that in this application, grid voltage drops can also be referred to as transient grid voltage drops. Both the grid voltage and the modulation wave are sinusoidal waves. The grid voltage and modulation wave not being in the same half-cycle can be understood as the positive amplitude of the grid voltage and the positive amplitude of the modulation wave not being in the same half-cycle, or the negative amplitude of the grid voltage and the negative amplitude of the modulation wave not being in the same half-cycle. Furthermore, a half-cycle can be divided into a positive half-cycle and a negative half-cycle. Taking a sine wave with a period of 360° as an example, the positive half-cycle can be from 0 to 180°, and the negative half-cycle can be from 180° to 360°. Currently, photovoltaic power plants typically determine whether the grid voltage has dropped by detecting changes in the amplitude or phase of the grid voltage.

[0031] However, dynamic changes in the power grid and high / low voltage ride-through events can also cause changes in the voltage amplitude of the grid. In both cases, the inverter should be able to operate normally without triggering grid voltage dip protection. Therefore, simply detecting the grid voltage amplitude cannot accurately distinguish between dynamic changes in the grid, high / low voltage ride-through events, and grid voltage dips caused by faults, nor can it accurately and effectively implement grid voltage dip protection strategies. Dynamic changes in the power grid refer to the characteristics of the grid's operating state changing over time, manifested as real-time fluctuations in parameters such as voltage, power, and frequency. For example, during peak electricity consumption periods, a surge in load can cause a drop in the grid voltage amplitude. According to national standards, inverters must possess corresponding high / low voltage ride-through capabilities; for example, when the grid voltage amplitude experiences an abnormal drop or rise, the inverter should be able to maintain continuous grid-connected operation and actively support the grid's recovery to stability.

[0032] Since the control response of the inverter's phase-locked loop is later than the grid voltage drop, there is a certain delay in judging whether the grid voltage has dropped based on the grid voltage phase. Therefore, it is impossible to accurately and effectively determine whether the grid voltage has dropped and to execute the grid voltage drop protection strategy.

[0033] In view of this, this application provides a method and related equipment for detecting grid voltage dips in photovoltaic inverters. Based on the characteristic that the grid voltage and modulation wave are in the same positive or negative half-cycle under normal grid-connected conditions, but will not be in the same half-cycle when the grid voltage dips due to a fault, this application proposes a technical solution for detecting whether an AC grid voltage dip has occurred based on the modulation wave and the sampled voltage of the AC grid. The technical solution provided by this application can improve the accuracy of detecting whether a grid voltage dip has occurred and improve the operational reliability of the power modules in the photovoltaic inverter.

[0034] The following is combined with Figure 1 and Figure 2 This application provides a detailed description of the technical solution provided.

[0035] Figure 1 This application provides a schematic topology diagram of a single-phase capacitive load switching in a photovoltaic power station. Figure 1 The photovoltaic power station 100 shown includes: photovoltaic modules (PV), photovoltaic inverters, and AC power grid. Figure 1 When the relay is in the closed state, it indicates that the photovoltaic inverter is in grid-connected state. At this time, the inverter will follow the voltage, frequency and phase of the AC grid and output an AC voltage that matches the AC grid.

[0036] like Figure 1As shown, when a capacitive load is switched on or off on the AC side of the photovoltaic inverter (point A in the figure), the impedance of the lines in the photovoltaic inverter changes, which may cause a voltage drop in the AC grid. This leads to a sudden change in the point of common coupling (PCC) voltage, which may result in a large current surge that could damage the power modules of the photovoltaic inverter (T1 to T4 in the figure). In this application, the point of common coupling refers to the common connection point between the photovoltaic inverter and the AC grid in the photovoltaic power plant system.

[0037] Therefore, in order to distinguish it from the dynamic changes of the power grid itself and the high and low voltage ride-through requirements, this application designs a detection method based on the modulation wave and the sampled voltage of the AC power grid to detect whether the voltage of the AC power grid has dropped.

[0038] Figure 2 This is a schematic flowchart illustrating a method for detecting grid voltage dips provided in this application. Figure 2 As shown, the detection method includes steps S210 to S230. In some embodiments, the detection method may further include step S240.

[0039] In this application, the method can be executed by a photovoltaic inverter, for example by hardware and / or software modules in the photovoltaic inverter, and this application does not impose any specific limitations on this.

[0040] S210 collects the voltage of the AC power grid at a preset frequency to obtain the sampled voltage. The AC power grid is connected to the AC side of the photovoltaic inverter.

[0041] When the photovoltaic inverter is in grid-connected state, the voltage of the AC grid can be collected by measuring the port voltage of the photovoltaic inverter.

[0042] In this application, the voltage of the AC power grid can be collected in real time at a preset frequency to obtain a sampled voltage. Optionally, considering that the voltage drop of the AC power grid occurs instantaneously, the voltage of the AC power grid can be collected at a high frequency, such as 500 kHz.

[0043] S220 determines the modulation wave of the photovoltaic inverter based on the phase of the sampled voltage.

[0044] In this application, the phase of the sampled voltage can be determined by using the phase-locked loop of the photovoltaic inverter, and the modulation wave of the photovoltaic inverter can be determined based on the phase of the sampled voltage. For details, please refer to the foregoing description, which will not be repeated here.

[0045] S230 determines whether the voltage of the AC power grid has dropped based on the sampled voltage and the modulated wave.

[0046] After determining the sampling voltage and modulation wave, it is possible to further determine whether the AC grid voltage has dropped based on the characteristic that the AC grid voltage and modulation wave are in the same positive or negative half-cycle under normal grid connection conditions, while the AC grid voltage will not be in the same half-cycle as the modulation wave when it drops due to a fault.

[0047] For example, a voltage drop in the AC mains can be determined by detecting whether the sampled voltage and the modulation wave are in the same half-cycle. If the sampled voltage and the modulation wave are in the same half-cycle, the AC mains is operating normally, meaning the voltage has not dropped; if they are not in the same half-cycle, the AC mains voltage has dropped. It should be noted that the sampled voltage not being in the same half-cycle includes situations where the AC mains voltage abruptly changes from a positive half-cycle to a negative half-cycle, resulting in the sampled voltage being in the negative half-cycle and the modulation wave in the positive half-cycle; or, the AC mains voltage abruptly changes from a negative half-cycle to a positive half-cycle, resulting in the sampled voltage being in the positive half-cycle and the modulation wave in the negative half-cycle.

[0048] Considering that during high-voltage ride-through events in AC power grids, the voltage and modulation waveform may not be in the same half-cycle for a short period, but the voltage change during a high-voltage ride-through is less than the voltage drop caused by a fault, a protection threshold can be further set to distinguish between high-voltage ride-through events and voltage drops caused by faults in the AC power grid. This improves the accuracy of detecting voltage drops caused by faults in the AC power grid.

[0049] For example, it can be further determined whether the absolute value of the sampled voltage is greater than or equal to the absolute value of the protection threshold. If the sampled voltage and the modulation wave are not in the same half-cycle, and the absolute value of the sampled voltage is greater than or equal to the absolute value of the protection threshold, it indicates that the voltage of the AC power grid has dropped. The sign of the protection threshold is opposite to the sign of the half-cycle in which the modulation wave is located, and the absolute value of the protection threshold is greater than 0.

[0050] For example, when the modulation wave is in the positive half-cycle, the protection threshold can be T1, and T1 < 0. If the sampled voltage is in the negative half-cycle and the value of the sampled voltage is less than the protection threshold T1, it can be considered that the voltage of the AC power grid has dropped. When the modulation wave is in the negative half-cycle, the protection threshold can be T2, and T2 > 0. If the sampled voltage is in the positive half-cycle and the value of the sampled voltage is greater than the protection threshold T2, it can be considered that the voltage of the AC power grid has dropped.

[0051] S240 executes the AC grid voltage drop protection strategy when the AC grid voltage drops.

[0052] Voltage drop protection strategies can include shutdown.

[0053] Optionally, the protection threshold can also be related to the maximum current capability of the power module in the photovoltaic inverter to shorten the detection time of a voltage drop in the AC grid, thereby shortening the time for implementing the AC grid voltage drop protection strategy, which in turn reduces the probability of damage to the power module in the photovoltaic inverter and improves the service life of the power module in the photovoltaic inverter.

[0054] In this application, when the voltage of the AC power grid does not drop, or when the AC power grid is in normal operation, S210 to S240 can be repeatedly executed to achieve real-time detection of the AC power grid voltage.

[0055] The technical solution provided in this application obtains a sampled voltage by high-frequency acquisition of the AC grid voltage, and determines whether a voltage drop has occurred by detecting the sampled voltage and the modulation wave, thereby protecting the photovoltaic inverter. The solution also sets a protection threshold; a voltage drop is only confirmed when the AC grid voltage drops and the absolute value of the sampled voltage exceeds the absolute value of the protection threshold, at which point a voltage drop protection strategy is executed. This solution can distinguish between dynamic changes in the grid and high / low voltage ride-through events, thus improving the accuracy of determining whether a voltage drop has occurred in the AC grid and effectively protecting the photovoltaic inverter, extending the lifespan of the power modules in the photovoltaic inverter. Furthermore, this solution can quickly and accurately detect AC grid voltage drops during the dynamic response of the phase-locked loop (PLL) without requiring additional components, reducing implementation difficulty and cost.

[0056] This application also provides a photovoltaic inverter for implementing the detection method described in the foregoing embodiments.

[0057] This application also provides a computer program product, for example, for detecting whether a voltage drop has occurred in the AC power grid. This computer program product can run on a processor to implement the method implemented by the photovoltaic inverter in the foregoing embodiments. Some embodiments of this application also provide a computer-readable storage medium containing computer instructions that, when run on a processor, can implement the method implemented by the photovoltaic inverter in any of the above embodiments.

[0058] The term "multiple" in this document refers to two or more. The character " / " generally indicates an "or" relationship between related objects; in formulas, " / " indicates a "division" relationship between related objects. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or order.

[0059] It is understood that, in the embodiments of this application, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0060] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for detecting grid voltage dips, applied to a photovoltaic inverter in grid-connected mode, characterized in that, The method includes: The voltage of the AC power grid is collected at a preset frequency to obtain the sampling voltage. The AC power grid is connected to the AC side of the photovoltaic inverter. The modulation wave of the photovoltaic inverter is determined based on the phase of the sampled voltage; The voltage of the AC power grid is determined based on the sampled voltage and the modulated wave.

2. The detection method according to claim 1, characterized in that, The step of determining whether the voltage of the AC power grid has dropped based on the sampled voltage and the modulated wave includes: Detect whether the sampling voltage and the modulation wave are in the same half-cycle; If the sampled voltage and the modulated wave are in the same half-cycle, then the AC power grid is determined to be in normal operating condition. If the sampled voltage and the modulated wave are not in the same half-cycle, it is determined that the voltage of the AC power grid has dropped.

3. The detection method according to claim 2, characterized in that, The method further includes: Determine whether the absolute value of the sampled voltage is greater than or equal to the absolute value of the protection threshold; If the sampled voltage and the modulation wave are not in the same half-cycle, and the absolute value of the sampled voltage is greater than or equal to the absolute value of the protection threshold, then the voltage of the AC power grid has dropped.

4. The detection method according to claim 3, characterized in that, The sign of the protection threshold is opposite to the sign of the half-cycle in which the modulation wave is located, and the absolute value of the protection threshold is greater than 0.

5. The detection method according to claim 4, characterized in that, The protection threshold is also related to the maximum current capability of the power module in the photovoltaic inverter.

6. The detection method according to any one of claims 1 to 5, characterized in that, The method further includes: The phase of the sampled voltage is determined by using the phase-locked loop of the photovoltaic inverter to lock the sampled voltage in phase.

7. The detection method according to any one of claims 1 to 5, characterized in that, The method further includes: When the voltage of the AC power grid drops, the voltage drop protection strategy of the AC power grid is executed.

8. An inverter, characterized in that, It includes various functional modules for implementing the method as described in any one of claims 1 to 7.

9. A computer-readable medium, characterized in that, The computer-readable medium stores program code for computer execution, the program code including instructions for performing the method as described in any one of claims 1 to 7.

10. A computer program product, characterized in that, It includes computer program code that, when run on a computer, causes the computer to perform the method as described in any one of claims 1 to 7.

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