A method for fast recovery control of active current after low voltage ride-through

Abstract

The present invention relates to the field of power grid technology, and discloses a method for quickly recovering active current after low voltage ride-through. The key points of the technical solution are as follows: before the low voltage ride-through, the power generation system passes the bus reference voltage through a low-pass filter to obtain a filter value; before the low voltage ride-through, the power generation system passes the bus reference voltage through a low-pass filter to obtain a filter value; and after the low voltage ride-through, the filter value is assigned to the bus reference voltage, so that the bus reference voltage after the low voltage ride-through is the same as the bus reference voltage before the low voltage ride-through, so that the output current is consistent, the recovery speed of the active current is improved, and the bus reference voltage is assigned with a corresponding assignment step ratio according to different assignment times, which can prevent the output current value from increasing instantaneously after exiting the low voltage ride-through mode to a certain extent.

Description

Technical Field

[0001] The present invention relates to the technical field of power grids, and more particularly to a method for quickly recovering active current after low voltage ride-through. Background Art

[0002] Low voltage ride-through is the ability of a small power generation system to withstand a certain limit of low voltage in the power grid within a certain period of time without exiting operation;

[0003] When the traditional low voltage ride-through is restored, its bus reference voltage is determined by the PV voltage at the input end and the AC voltage at the output end, while the PV voltage at the output end is determined by MPPT tracking. MPPT tracking takes one second, resulting in slow changes in the PV voltage at the input end, slow changes in the bus reference voltage, and slow recovery of active current. Summary of the invention

[0004] In view of the deficiencies in the prior art, the object of the present invention is to provide a method for quickly recovering active current after low voltage ride-through, so as to quickly realize the recovery of active current.

[0005] To achieve the above object, the present invention provides the following technical solution: A method for quickly recovering active current after low voltage ride-through, comprising the following steps: S1: before low voltage ride-through, the power generation system passes the bus reference voltage through a low-pass filter to obtain a filtered value;

[0006] S2: preset a saving time, when the low voltage ride-through enters the saving time, the filter value is saved and the low voltage ride-through mode is entered immediately;

[0007] S3: After exiting the low voltage ride-through mode, entering the recovery mode, the filter value is assigned to the bus reference voltage.

[0008] As a further improvement of the present invention, a locking time limit is preset, and after the low voltage ride-through mode is exited, the locking time limit passes so that the phase-locked loop locks the phase between the input voltage and the output voltage.

[0009] As a further improvement of the present invention, the locking time limit ranges from 30 ms to 60 ms.

[0010] As a further improvement of the present invention, an assignment link is preset in the recovery mode, and an assignment table is preset in the assignment link. The assignment table records the assignment time and the assignment step ratio corresponding to the assignment time. The bus reference voltage is assigned according to different assignment times and the corresponding assignment step ratio.

[0011] As a further improvement of the present invention, the assignment time range is 0 to 50 ms.

[0012] As a further improvement of the present invention, the assignment step ratio decreases as the value within a single assignment time increases.

[0013] As a further improvement of the present invention, an initial time and an assigned constant ratio corresponding to the initial time are preset in the recovery mode, and within the initial time, the bus reference voltage is assigned with the corresponding assigned constant ratio.

[0014] As a further improvement of the present invention, the absolute value of the difference between the initial time and the assignment time is a time difference, and within the time difference, the bus reference voltage is assigned with the corresponding assignment time and the corresponding assignment step ratio.

[0015] Beneficial effects of the present invention: before low voltage crossing, the power generation system in the present invention passes the bus reference voltage through a low-pass filter to obtain a filtered value, and after the low voltage crossing, the filtered value is assigned to the bus reference voltage, so that the bus reference voltage after the low voltage crossing is the same as the bus reference voltage before the low voltage crossing, so that the output current is consistent, the recovery speed of the active current is improved, and the bus reference voltage is assigned according to different assignment times with corresponding assignment step ratios, which can prevent the output current value from increasing instantaneously after exiting the low voltage crossing mode to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The same parts are represented by the same reference numerals. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the accompanying drawings, and the words "bottom surface" and "top surface", "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0018] Reference Figure 1 As shown, a method for quickly recovering active current after low voltage crossing of this embodiment includes the following steps: S1: before low voltage crossing, the power generation system passes the bus reference voltage through a low-pass filter, and only passes through one low-pass filter to obtain a filtered value; the filtered value represents the actual voltage value of the bus reference voltage.

[0019] S2: preset save time, which can be 0. The save time provides a time for saving the filter value. When the low voltage ride-through enters the save time, the filter value is saved and the low voltage ride-through mode is entered immediately.

[0020] S3: After exiting the low voltage ride-through mode, enter the recovery mode, which is to assign the filter value to the bus reference voltage. The filter value is saved, and after the low voltage ride-through, the bus reference voltage is operated according to its actual voltage value before the low voltage ride-through, so that the actual value of the bus reference voltage is stable before and after the low voltage ride-through, and the recovery speed of the active current is improved.

[0021] The preset locking time limit, after exiting the low voltage ride-through mode, the locking time limit is passed so that the phase-locked loop can lock the phase between the input voltage and the output voltage. The locking time limit ranges from 30ms to 60ms. Specifically, the locking time limit can be set to 40ms, which can ensure that the phase-locked loop completely locks the phase between the input voltage and the output voltage. The working principle of the phase-locked loop is to detect the phase difference between the input signal and the output signal, and convert the detected phase difference into a voltage signal output through a phase detector. After filtering by a low-pass filter, a control voltage of a voltage-controlled oscillator is formed, and the frequency of the oscillator output signal is controlled. Then, the frequency and phase of the oscillator output signal are fed back to the phase detector through a feedback path. During the operation of the phase-locked loop, when the frequency of the output signal proportionally reflects the frequency of the input signal, the output voltage and the input voltage maintain a fixed phase difference, so that the phase of the input voltage and the output voltage is locked. The setting of the locking time limit makes the output voltage more stable, thereby stabilizing the output current.

[0022] An assignment link is preset in the recovery mode, and an assignment table is preset in the assignment link. The assignment time and the assignment step ratio corresponding to the assignment time are recorded in the assignment table. The assignment time range is 0 to 50ms. As an assignment time goes by, the assignment time is divided into several time intervals. The assignment step ratio is set from large to small from the first time interval to the last time interval, or the ratio can be evenly set from the first time interval to the last time interval. Of course, it can also be set from small to large. The bus reference voltage is assigned with the corresponding assignment step ratio according to different assignment times. For example, when the assignment time is 50ms, the assignment time is divided into 5 time intervals. The assignment step ratio can be set to 10%, 15%, 20%, 25% and 30% or 30%, 25%, 20%, 15% and 10% or all 10%, which can prevent the output current value from increasing instantaneously after exiting the low voltage ride-through mode to a certain extent.

[0023] The assignment step ratio decreases with the increase of the value within a single assignment time, which can control the initial output current not to increase instantly, and make the initial output current not very low, and tend to be stable within an assignment time, and the stable change continues to decrease. If the assignment step ratio increases with the increase of the value within a single assignment time, the initial output current will be very small, the output current will tend to increase rapidly, and it will also be unstable.

[0024] The recovery mode is preset with an initial time and a constant value ratio corresponding to the initial time. During the initial time, the bus reference voltage is assigned with the corresponding constant value ratio. The initial time is a period of time from the start of the assignment time, and its length must be less than the length of the assignment time. The initial time can be taken as 10ms. Within 10ms, the bus reference voltage is assigned with a constant value ratio. The constant value ratio can be 10%. Within 10ms, the initial time is set to 2 time intervals, that is, every 5ms is a time interval. In a time interval Within the interval, the bus reference voltage is assigned at a ratio of 10%. Within 10ms, the output current is prevented from increasing instantly, and the current is increased constantly. The absolute value of the difference between the initial time and the assignment time is the time difference. Within the time difference, the bus reference voltage is assigned with the corresponding assignment time and the corresponding assignment step ratio. If the assignment time is 50ms, the time difference is 40ms. The assignment table uses 40ms as the index and executes the corresponding assignment step ratio. In the first time interval after 10ms, the step can be greater than or equal to 10%.

[0025] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for quickly recovering active current after low voltage ride-through, characterized in that: The steps include: S1: Before low voltage ride-through, the power generation system passes the bus reference voltage through a low-pass filter to obtain a filtered value; S2: preset a saving time, when the low voltage ride-through enters the saving time, the filter value is saved and the low voltage ride-through mode is entered immediately; S3: After exiting the low voltage ride-through mode, the system enters the recovery mode and assigns the filter value to the bus reference voltage; A preset locking time limit, after exiting the low voltage ride-through mode, the locking time limit passes so that the phase-locked loop locks the phase between the input voltage and the output voltage; The locking time limit range is 30ms to 60ms; The recovery mode is preset with an assignment link, the assignment link is preset with an assignment table, the assignment table records the assignment time and the assignment step ratio corresponding to the assignment time, and the bus reference voltage is assigned with the corresponding assignment step ratio according to different assignment times; The assignment time range is 0 to 50ms; The ratio of the value assignment steps decreases as the value within the single value assignment time increases; The recovery mode is preset with an initial time and a constant value ratio corresponding to the initial time, and within the initial time, the bus reference voltage is assigned with the corresponding constant value ratio; The absolute value of the difference between the initial time and the assignment time is a time difference. Within the time difference, the bus reference voltage is assigned with the corresponding assignment time and the corresponding assignment step ratio.

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