Low voltage ride through response control method based on voltage threshold and duration

Abstract

The invention discloses a low-voltage ride-through response control method based on a voltage threshold and duration, and the method comprises the steps: collecting the three-phase voltages Ua, Ub and Uc of a power grid in real time, and calculating the equivalent voltage Um of a grid-connected point according to the three-phase voltages Ua, Ub and Uc of the power grid; a preset rated voltage Un is obtained, and an early warning mark position is determined based on the preset rated voltage Un, the equivalent voltage Um of the grid connection point and a preset fault ride-through judgment strategy, and the early warning mark position comprises 0 and 1; when the state that the early warning mark position is specifically 1 is kept continuously in a preset time period, the fault level is determined based on the equivalent voltage Um of the grid-connected point, the preset rated voltage Un and the fault level strategy, and the fault level comprises the first fault level and the second fault level; and regulating and controlling the power grid voltage according to the fault level. According to the low-voltage ride-through response control method based on the voltage threshold and the duration, the sensing and response speed of an operator to the state change of the power grid is improved, and the possibility of artificial delay is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid operation and maintenance, and in particular to a low voltage ride-through response control method based on voltage threshold and duration. Background Art

[0002] With the rapid development of renewable energy, the application of solar photovoltaic power generation methods is becoming more and more widespread. As the core equipment in photovoltaic power generation methods, the stable operation of grid-connected inverters is of vital importance to the safety and stability of the power grid. However, there are some problems at present. When a grid-connected inverter fails, it may have a certain impact on the power grid. Especially during the fault ride-through process, improper control may cause large fluctuations in parameters such as grid voltage and frequency, and even have adverse effects on the power grid.

[0003] At present, the fault ride-through control for grid-connected inverters mainly adopts control strategies based on voltage source inverters and current source inverters. These control strategies usually rely on the detection and feedback of parameters such as voltage and current to achieve control of the fault ride-through process. However, these solutions may have problems such as insufficient control or insufficient judgment conditions leading to slow response speed when dealing with complex fault conditions. Common insufficient control or insufficient judgment conditions are reflected in the following aspects:

[0004] Delayed voltage detection and response: Existing fault ride-through technologies for grid-connected inverters generally rely on traditional voltage and current detection methods, which may not be able to immediately identify voltage anomalies at the initial stage of a fault. For example, methods based on periodic sampling may miss short-term voltage drops, resulting in a delay in the method initiating necessary fault response measures. This delay is extremely detrimental to grid stability, especially in high-load or multi-source dynamic grid environments.

[0005] Insufficient judgment conditions: Most existing methods use fixed voltage thresholds (such as 90%, 80%, etc.) to determine when to trigger a low voltage ride-through response. This fixed threshold cannot effectively reflect the real-time status and changes of the power grid, and may cause the response to be too slow or overly sensitive. For example, when the grid voltage fluctuates naturally, the fixed threshold may mistakenly trigger a fault response or fail to initiate a response when necessary.

[0006] Inadaptability of control strategies: When an asymmetric voltage drop occurs in the power grid, existing fault handling strategies often only consider the simple reduction of active power or the compensation of reactive power, without adjusting the control strategy according to the specific characteristics of the voltage drop, such as the drop duration, drop speed and amplitude. Such a one-size-fits-all approach is incapable of handling complex or extreme power grid events and cannot effectively minimize the impact of the fault on the power grid. Summary of the invention

[0007] To solve the technical problems existing in the background art, the present invention proposes a low-voltage ride-through response control method based on voltage threshold and duration.

[0008] The low-voltage ride-through response control method based on voltage threshold and duration proposed by the present invention includes the following steps:

[0009] S1. Real-time collect the three-phase grid voltages Ua, Ub, and Uc, and calculate the equivalent voltage Um of the grid connection point according to the three-phase grid voltages Ua, Ub, and Uc.

[0010] S2. Obtain the preset rated voltage Un, and determine the warning flag position based on the preset rated voltage Un, the equivalent voltage Um of the grid connection point, and the preset fault ride-through determination strategy. The warning flag position includes 0 and 1.

[0011] S3. When the warning flag position is specifically in the state of 1 and continuously maintained within the preset time period, determine the fault level based on the equivalent voltage Um of the grid connection point, the preset rated voltage Un, and the fault level strategy. The fault levels include first-level fault and second-level fault.

[0012] S4. Regulate the grid voltage according to the fault level.

[0013] Preferably, the preset fault ride-through determination strategy specifically includes:

[0014] When the equivalent voltage Um of the grid connection point is less than 90% of the rated voltage Un, the warning flag position is set to 1, and the equivalent voltage Um of the grid connection point being less than 90% of the rated voltage Un is recorded as the first state.

[0015] When the equivalent voltage Um of the grid connection point is equal to 90% of the rated voltage Un, the warning flag position is set to 0, and the equivalent voltage Um of the grid connection point being equal to 90% of the rated voltage Un is recorded as the second state.

[0016] When, within the preset time threshold, the numerical relationship between the equivalent voltage Um of the grid connection point and the rated voltage Un returns from the first state to the second state, the warning flag position returns from 1 to 0.

[0017] Preferably, the fault level strategy specifically includes:

[0018] When, within the preset time period, the warning flag position is specifically in the state of 1 and continuously maintained, and 0.8Un < Um < 0.9Un, the fault level is specifically the first-level fault.

[0019] When, within the preset time period, the warning flag position is specifically in the state of 1 and continuously maintained, and Um < 0.8Un, the fault level is specifically the second-level fault.

[0020] Wherein, Um is the equivalent voltage of the grid connection point; Un is the preset rated voltage.

[0021] Preferably, the fault level is specifically the first-level fault; step S4 specifically includes:

[0022] When 0.8Un < Um < 0.9Un lasts for more than the first threshold, start the LVRT response to determine whether the voltage dip is symmetrical;

[0023] When the voltage dip is a symmetrical dip, implement the active power reduction control strategy;

[0024] When the voltage dip is an asymmetrical dip, implement the reactive power compensation adjustment strategy.

[0025] Preferably, the active power reduction control strategy is specifically to reduce the load of the system by reducing the output power of the generator or adjusting the absorption power of the load to help the power grid restore the normal voltage; that is, restore to Um = 0.9Un; the reactive power compensation adjustment strategy is specifically to balance the reactive power in the power grid through a static var generator or a capacitor so that the power grid restores the normal voltage, that is, restore to Um = 0.9Un.

[0026] Preferably, the fault level is specifically the second-level fault; step S4 specifically includes:

[0027] When Um < 0.8Un lasts for more than the second threshold, start the LVRT response to determine whether the voltage dip is symmetrical;

[0028] When the voltage dip is a symmetrical dip, implement the reactive power compensation strategy;

[0029] When the voltage dip is an asymmetrical dip, implement the reactive power compensation and voltage drop control strategy.

[0030] Preferably, the reactive power compensation strategy is specifically to balance the reactive power in the power grid through a static var generator or a capacitor so that the power grid restores the normal voltage, that is, restore to Um = 0.9Un; the reactive power compensation and voltage drop control strategy is specifically to balance the reactive power in the power grid through a static var generator or a capacitor, and at the same time start the response mechanism after the voltage dip. The response mechanism includes controlling the power transmission of the generator and reducing the load to ensure that the generator can operate normally during the voltage recovery process so that the power grid restores the normal voltage, that is, restore to Um = 0.9Un.

[0031] Preferably, the calculation process of the equivalent voltage Um of the grid connection point is as follows:

[0032]

[0033] Among them, Ua, Ub, and Uc are the three-phase voltages of the power grid collected in real time.

[0034] In the present invention, the proposed low voltage ride-through response control method based on voltage threshold and duration collects the three-phase voltages Ua, Ub, and Uc of the power grid in real time, and calculates the equivalent voltage Um of the grid connection point according to the three-phase voltages Ua, Ub, and Uc of the power grid; obtains the preset rated voltage Un, and determines the warning mark position based on the preset rated voltage Un, the equivalent voltage Um of the grid connection point, and the preset fault ride-through judgment strategy, and the warning mark position includes 0 and 1; when the warning mark position is specifically 1 and the state is continuously maintained within the preset time period, the fault level is determined based on the equivalent voltage Um of the grid connection point, the preset rated voltage Un, and the fault level strategy, and the fault level includes fault level 1 and fault level 2; according to the fault level, the grid voltage is regulated. Using the equivalent voltage Um of the grid connection point as an indicator for judging the voltage state can more accurately identify the change of the grid voltage and avoid misjudgment or delayed response. According to the symmetry and duration of the voltage drop, active power reduction or reactive power compensation is selectively implemented to quickly restore the stability of the grid. Setting up an automated early warning and response mechanism improves operators' perception and response speed to changes in grid status and reduces the possibility of human delays. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the working process structure of the low voltage ride through response control method based on voltage threshold and duration proposed by the present invention;

[0036] Figure 2 This is a schematic diagram of the implementation process structure of the low voltage ride through response control method based on voltage threshold and duration proposed by the present invention. DETAILED DESCRIPTION

[0037] Reference Figure 1 and Figure 2 The low voltage ride through response control method based on voltage threshold and duration proposed by the present invention comprises the following steps:

[0038] S1. Collect the three-phase voltages Ua, Ub and Uc of the power grid in real time, and calculate the equivalent voltage Um of the grid connection point based on the three-phase voltages Ua, Ub and Uc of the power grid.

[0039] In this embodiment, the calculation process of the equivalent voltage Um of the grid connection point is as follows:

[0040]

[0041] Among them, Ua, Ub, and Uc are the three-phase voltages of the power grid collected in real time.

[0042] In this embodiment, the three-phase voltages Ua, Ub, and Uc of the power grid are first collected to calculate the equivalent voltage Um of the grid connection point; when the equivalent voltage Um drops to 90% of the rated voltage Un, it is determined that the voltage drop is too large, but the LVRT response is not triggered, and the warning flag is set to 1. If the equivalent voltage Um recovers to more than 90% of the rated voltage Un within 5s, the warning flag is set to 0.

[0043] In this embodiment, the warning flag is set to 1, indicating that the voltage drop exceeds the normal range and there may be a risk of unstable operation of the power grid. The setting of this warning flag helps operators or automation systems to quickly detect potential problems and take further monitoring or adjustment measures.

[0044] S2. Obtain a preset rated voltage Un, and determine a warning mark position based on the preset rated voltage Un, the equivalent voltage Um of the grid connection point, and a preset fault ride-through determination strategy. The warning mark position includes 0 and 1.

[0045] In this embodiment, the preset fault ride-through determination strategy specifically includes:

[0046] When the equivalent voltage Um of the grid connection point is less than 90% of the rated voltage Un, the warning mark position is set to 1, and the equivalent voltage Um of the grid connection point is less than 90% of the rated voltage Un as the first state;

[0047] When the equivalent voltage Um of the grid connection point is equal to 90% of the rated voltage Un, the warning mark position is set to 0, and the equivalent voltage Um of the grid connection point is equal to 90% of the rated voltage Un as the second state;

[0048] When the numerical relationship between the equivalent voltage Um and the rated voltage Un of the grid connection point is restored from the first state to the second state within the preset time threshold, the position of the warning mark is restored from 1 to 0.

[0049] In this embodiment, if the equivalent voltage Um can recover to more than 90% of the rated voltage Un within the next 5 seconds, the system will automatically reset the warning flag to 0, indicating that the voltage has returned to the normal range and the grid stability has been restored.

[0050] S3. When the warning mark position is maintained at 1 for a preset time period, the fault level is determined based on the equivalent voltage Um of the grid connection point, the preset rated voltage Un, and the fault level strategy. The fault levels include level 1 and level 2.

[0051] In this embodiment, the fault level strategy specifically includes:

[0052] When the state where the warning flag position is specifically 1 lasts and 0.8Un < Um < 0.9Un within a preset time period, the fault level is specifically the first-level fault;

[0053] When the state where the warning flag position is specifically 1 lasts and Um < 0.8Un within a preset time period, the fault level is specifically the second-level fault;

[0054] Among them, Um is the equivalent voltage of the grid connection point; Un is the preset rated voltage.

[0055] In this embodiment, it is detected that the equivalent voltage Um is lower than 90% of the rated voltage Un but higher than 80% of the rated voltage Un (0.8Un < Um < 0.9Un), that is, the first-level fault. At this time, it is judged whether the voltage dip time exceeds 3 s to ensure that the voltage reduction is continuous. If it does not exceed 3 s, no corresponding action is triggered and it is determined as a temporary grid fluctuation. If it exceeds 3 s, the LVRT response is triggered, and it is detected and judged whether the voltage dip is symmetric. If the voltage dip is symmetric, the active power reduction control strategy is introduced until the low voltage ride through ends. If the voltage dip is asymmetric, reactive power compensation regulation is introduced until the low voltage ride through ends.

[0056] In this embodiment, it is detected that the equivalent voltage Um is lower than 80% of the rated voltage Un (Um < 0.8Un), that is, the second-level fault. At this time, it is judged whether the voltage dip time exceeds 3 s to ensure that the voltage reduction is continuous. If it does not exceed 3 s, no corresponding action is triggered and it is determined as a temporary grid fluctuation. If it exceeds 3 s, the LVRT (low voltage ride through) response is triggered, and it is detected and judged whether the voltage dip is symmetric. Due to the large voltage dip amplitude, if the voltage dip is symmetric, the reactive power compensation strategy is directly introduced until the low voltage ride through ends. If the voltage dip is asymmetric, while introducing reactive power compensation regulation, voltage drop control is increased until the low voltage ride through ends.

[0057] S4. Regulate the grid voltage according to the fault level.

[0058] In this embodiment, the LVRT response is the low voltage ride through response.

[0059] In this embodiment, the fault level is specifically the first-level fault; step S4 specifically includes:

[0060] When 0.8Un < Um < 0.9Un lasts for more than the first threshold, start the LVRT response to judge whether the voltage dip is symmetric;

[0061] When the voltage dip is a symmetric dip, implement the active power reduction control strategy;

[0062] When the voltage dip is an asymmetric dip, implement the reactive power compensation regulation strategy.

[0063] In this embodiment, the active power reduction control strategy is specifically to reduce the load of the system by reducing the output power of the generator or adjusting the absorbed power of the load to help the power grid restore normal voltage; that is, restore to Um=0.9Un; the reactive power compensation adjustment strategy is specifically to balance the reactive power in the power grid through a static reactive generator or a capacitor, so that the power grid restores normal voltage, that is, restores to Um=0.9Un.

[0064] In this embodiment, the above control strategy will continue until the voltage recovers to more than 90% of the rated voltage Un. Once it is detected that Um reaches or exceeds this level again, the system will stop the LVRT response and resume normal operation.

[0065] In this embodiment, the fault level is specifically fault level 2; step S4 specifically includes:

[0066] When Um<0.8Un continuously exceeds the second threshold, the LVRT response is initiated to determine whether the voltage drop is symmetrical;

[0067] When the voltage drop is symmetrical, the reactive power compensation strategy is implemented;

[0068] When the voltage drop is asymmetrical, reactive power compensation and voltage drop control strategies are implemented.

[0069] In this embodiment, the reactive power compensation strategy is specifically to balance the reactive power in the power grid through a static reactive generator or a capacitor so that the power grid can restore the normal voltage, that is, restore to Um=0.9Un; the reactive power compensation and voltage drop control strategy is specifically to balance the reactive power in the power grid through a static reactive generator or a capacitor, and at the same time start the response mechanism after the voltage drop, the response mechanism includes controlling the power delivery of the generator and reducing the load to ensure that the generator can operate normally during the voltage recovery process, so that the power grid can restore the normal voltage, that is, restore to Um=0.9Un.

[0070] In this embodiment, the reactive power compensation and voltage drop control strategy supports the grid by adjusting the output to increase reactive power when the voltage drops. It is necessary to output positive or negative reactive power and adjust the current phase to provide the voltage support required by the grid. To avoid equipment damage, the active power output is usually reduced when the voltage drops. This dynamic adjustment can protect the stability of the inverter and other grid equipment. According to the change of voltage level, the active output will be flexibly adjusted to ensure system safety.

[0071] In this embodiment, when the voltage drop is at the second level of the fault, the reactive power compensation mode is preferentially switched. This mechanism ensures that a quick response can be made to reduce the system burden when the grid load suddenly increases or the voltage drops rapidly. There is a close correlation between reactive power compensation and voltage drop control. The responses of the two are carried out synchronously. When reactive power compensation is started, the voltage drop will be accompanied by a reduction in active power output. Through this coordination, not only can the grid voltage recovery be supported, but the grid load can also be reduced to a certain extent, alleviating the voltage pressure. The main goal of the reactive power compensation and voltage drop control strategy is to effectively manage the reactive power in the grid to cope with the situation of rapid voltage drop and ensure the stability and reliability of the grid under fault conditions. At the same time, the response mechanism after the voltage drop is activated to maintain the normal operation of the generator and realize the recovery of the grid voltage.

[0072] In this embodiment, the above control strategy will continue until the Um voltage recovers to more than 80% of the rated voltage Un. Once it is detected that Um reaches or exceeds this level again, the system will automatically stop the LVRT response and resume normal operation.

[0073] In the specific working process of the low voltage ride-through response control method based on voltage threshold and duration of this embodiment, Um is used as an indicator to judge the voltage state, which can more accurately identify the change of grid voltage and avoid misjudgment or delayed response. According to the symmetry and duration of the voltage drop, active power reduction or reactive power compensation is selectively implemented to quickly restore grid stability. An automated early warning and response mechanism is set up to improve the operator's perception and response speed to changes in grid status and reduce the possibility of human delays.

[0074] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A low voltage ride-through response control method based on voltage threshold and duration, characterized in that: It includes the following steps: S1. Collect the three-phase grid voltages Ua, Ub, and Uc in real time, and calculate the equivalent voltage Um of the grid connection point based on the three-phase grid voltages Ua, Ub, and Uc; S2. Obtain the preset rated voltage Un, and determine the warning flag position based on the preset rated voltage Un, the equivalent voltage Um of the grid connection point, and the preset fault ride-through determination strategy. The warning flag position includes 0 and 1; S3. When the warning flag position is specifically in the state of 1 and continuously maintained within the preset time period, determine the fault level based on the equivalent voltage Um of the grid connection point, the preset rated voltage Un, and the fault level strategy. The fault level includes Fault Level 1 and Fault Level 2; S4. Regulate the grid voltage according to the fault level.

2. The low voltage ride through response control method based on voltage threshold and duration according to claim 1, characterized in that: The preset fault ride-through determination strategy specifically includes: When the equivalent voltage Um of the grid connection point is less than 90% of the rated voltage Un, set the warning flag position to 1, and record the situation that the equivalent voltage Um of the grid connection point is less than 90% of the rated voltage Un as the first state; When the equivalent voltage Um of the grid connection point is equal to 90% of the rated voltage Un, set the warning flag position to 0, and record the situation that the equivalent voltage Um of the grid connection point is equal to 90% of the rated voltage Un as the second state; When within the preset time threshold, the numerical relationship between the equivalent voltage Um of the grid connection point and the rated voltage Un returns from the first state to the second state, the warning flag position returns from 1 to 0.

3. The low voltage ride through response control method based on voltage threshold and duration according to claim 1, characterized in that: The fault level strategy specifically includes: When within the preset time period, the warning flag position is specifically in the state of 1 and continuously maintained, and 0.8Un < Um < 0.9Un, the fault level is specifically Fault Level 1; When within the preset time period, the warning flag position is specifically in the state of 1 and continuously maintained, and Um < 0.8Un, the fault level is specifically Fault Level 2; Wherein, Um is the equivalent voltage of the grid connection point; Un is the preset rated voltage.

4. The low voltage ride through response control method based on voltage threshold and duration according to claim 1, characterized in that: The fault level is specifically Fault Level 1; Step S4 specifically includes: When 0.8Un < Um < 0.9Un lasts for more than the first threshold, start the LVRT response to determine whether the voltage dip is symmetrical; When the voltage dip is a symmetrical dip, implement the active power reduction control strategy; When the voltage dip is an asymmetrical dip, implement the reactive power compensation regulation strategy.

5. The low voltage ride through response control method based on voltage threshold and duration according to claim 4, characterized in that: The active power reduction control strategy is specifically to reduce the load of the system by reducing the output power of the generator or adjusting the absorption power of the load to help the grid restore the normal voltage, that is, restore to Um = 0.9Un; the reactive power compensation regulation strategy is specifically to balance the reactive power in the grid through a static var generator or a capacitor to make the grid restore the normal voltage, that is, restore to Um = 0.9Un.

6. The low voltage ride through response control method based on voltage threshold and duration according to claim 1, characterized in that: The fault level is specifically Fault Level 2; Step S4 specifically includes: When Um < 0.8Un lasts for more than the second threshold, start the LVRT response to determine whether the voltage dip is symmetrical; When the voltage dip is a symmetrical dip, implement the reactive power compensation strategy; When the voltage dip is an asymmetrical dip, implement the reactive power compensation and voltage drop control strategy.

7. The low voltage ride through response control method based on voltage threshold and duration according to claim 6, characterized in that: The reactive power compensation strategy is specifically to balance the reactive power in the power grid through a static reactive generator or a capacitor so that the power grid can restore to normal voltage, that is, restore to Um=0.9Un; the reactive power compensation and voltage drop control strategy is specifically to balance the reactive power in the power grid through a static reactive generator or a capacitor; at the same time, the response mechanism after the voltage drop is started, and the response mechanism includes controlling the power delivery of the generator and reducing the load to ensure that the generator can operate normally during the voltage recovery process, so that the power grid can restore to normal voltage, that is, restore to Um=0.9Un.

8. The low voltage ride through response control method based on voltage threshold and duration according to claim 1, characterized in that: The calculation process of the equivalent voltage Um at the grid connection point is as follows: Among them, Ua, Ub, and Uc are the three-phase voltages of the power grid collected in real time.

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