A voltage sag detection method considering speed and anti-interference capability

Abstract

The application discloses a voltage sag detection method considering speed and anti-interference capability, and relates to the technical field of circuit device control of alternating current transmission and distribution network. The application provides a new method for detecting voltage sag. Without changing original hardware equipment, the voltage effective value fast algorithm can quickly and reliably detect voltage sag.

Description

Technical Field

[0001] This invention relates to the field of circuit device technology for AC power transmission and distribution networks, and more particularly to a voltage sag detection method that balances speed and anti-interference capability, and a low voltage detection and judgment process for a dynamic voltage restorer (DVR) device. Background Technology

[0002] In power systems, short-circuit faults, the starting of large-capacity induction motors, transformer commissioning, and lightning strikes are the main causes of voltage sags. With rapid economic development, sophisticated and complex electronic devices are increasingly used in modern industry. These devices are highly sensitive to short-term voltage sags; even a voltage sag or interruption lasting only tens of milliseconds can disrupt their normal operation, leading to significant economic losses and safety hazards. Therefore, voltage sags and interruptions have become the most critical power quality issues across various sectors, seriously threatening normal and safe electricity use and the rapid development of the national economy. They represent a new challenge for power grid companies and industrial and commercial electricity users. Summary of the Invention

[0003] This invention primarily addresses the shortcomings of existing technologies by providing a method for calculating the voltage amplitude U using a 1 / 4 cycle voltage. rms The calculated voltage amplitude is repeatedly assessed to determine whether the system is under low voltage conditions. This method balances the speed and anti-interference requirements of DVRs and can be well applied to practical engineering applications requiring voltage sag detection.

[0004] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions:

[0005] A voltage sag detection method that balances speed and anti-interference capability calculates the voltage amplitude Urms using a 1 / 4 cycle voltage and then repeatedly judges whether the calculated voltage amplitude indicates a low voltage condition in the system.

[0006] As a preferred method, the effective value Urms of the system voltage is calculated.

[0007] Preferably, the amplitude of the system voltage is calculated using a 1 / 4 cycle sliding window.

[0008] Preferably, the amplitude Urms of the system voltage is calculated by obtaining the root mean square value U1 / 4rms of the 1 / 4 cycle and the sinδ and cosδ of the phase angle δ, where sinδ and cosδ can be obtained in real time by the phase-locked loop.

[0009] As a preferred method, the delay is 2ms when used to detect the 90% voltage dip commonly used in engineering practice.

[0010] Preferably, assuming the single-phase voltage is

[0011] (1)

[0012] Among them, U rms This represents the effective value of the voltage period.

[0013] According to the definition of the effective value of a continuous periodic signal, the root mean square value of the voltage during a quarter cycle can be expressed as:

[0014] (2)

[0015] Among them, U 1 / 4rms The effective value of the voltage is 1 / 4 cycle, and δ is from 0 to... Any value between.

[0016] Substituting equation (1) into equation (2) yields

[0017] (3)

[0018] From equation (3), we can obtain

[0019] (4)

[0020] because

[0021] (5)

[0022] Combining equations (4) and (5) yields

[0023] (6)

[0024] From equation (6), it can be seen that we only need to find U 1 / 4rms By combining Sinδ and Cosδ, we can obtain U. rms Sinδ and Cosδ can be calculated in real time by the phase-locked loop, U 1 / 4rms It can be obtained from equation (7).

[0025] (7).

[0026] Dynamic voltage restorers (DVRs) have gradually become the most effective and economical power equipment for managing voltage sags due to their advantages such as wide compensation range, high efficiency, good economy, and reliability.

[0027] As a key technology in DVRs, the speed and accuracy of voltage sag detection are crucial to the compensation effect of DVRs. To date, various voltage sag detection methods have been proposed, mainly including the RMS algorithm, peak voltage method, missing voltage method, single-phase voltage derivative method, and algorithms based on dq transform and its improvements. The RMS algorithm is simple to calculate, easy to implement, and has strong noise resistance, but it requires at least half a cycle of historical data, has poor real-time performance, and cannot provide the start and end times of the voltage sag or calculate possible phase transitions. The peak voltage method is simple in principle, easy to implement, and can quickly detect voltage recovery after the sag ends, reflecting the start and end times of the voltage sag. However, this method requires half a cycle to acquire sag information, and the detected sag amplitude is generally larger than the actual value, so the detection result will have a large error when the sag amplitude is close to the rated value. The missing voltage method is similar in principle to a phase-locked loop; the missing voltage value is the difference between the instantaneous ideal voltage value and the instantaneous actual voltage value. This method cannot clearly determine the start time of a voltage sag and cannot effectively detect accurate voltage sag characteristics. The single-phase voltage derivative method can simultaneously obtain the amplitude and phase of the voltage sag, but the derivative calculation itself introduces significant errors to both voltage fluctuations and harmonics. Furthermore, the closer the sampling points are, the worse the resistance to white noise; the farther apart the sampling points are, the less accurate the derivative obtained by the difference method. The dq transformation method based on instantaneous reactive power theory is only applicable to three-phase symmetrical systems, while voltage sags in the power grid are usually single-phase or two-phase fluctuations, and three-phase symmetrical sags are rare. In addition, the delay of the low-pass filter further limits the applicability of the traditional dq transformation method, requiring further improvement. The improved single-phase dq transformation method uses derivatives to construct a virtual three-phase system and separate the DC component in the dq coordinate system. Although this avoids the delay of constructing a virtual three-phase system and the low-pass filter, improving real-time performance, it still faces the challenge of selecting the sampling point interval. Detailed Implementation

[0028] The technical solution of the present invention will be further described in detail below through embodiments.

[0029] Example 1: A voltage sag detection method that balances speed and anti-interference capability. The voltage amplitude Urms is calculated using a 1 / 4 cycle voltage, and the calculated voltage amplitude is repeatedly judged to determine whether the system is in a low voltage condition.

[0030] The effective value Urms of the system voltage is calculated.

[0031] The amplitude of the system voltage is calculated using a 1 / 4 cycle sliding window.

[0032] The amplitude Urms of the system voltage is calculated by using the root mean square value U1 / 4rms of the 1 / 4 cycle and the sinδ and cosδ of the phase angle δ. The sinδ and cosδ can be obtained in real time by the phase-locked loop.

[0033] The delay is 2ms when used to detect the 90% voltage sag commonly used in engineering practice.

[0034] Assume the single-phase voltage is

[0035] (1)

[0036] Among them, U rms This represents the effective value of the voltage period.

[0037] According to the definition of the effective value of a continuous periodic signal, the root mean square value of the voltage during a quarter cycle can be expressed as:

[0038] (2)

[0039] Among them, U 1 / 4rms The effective value of the voltage is 1 / 4 cycle, and δ is from 0 to... Any value between.

[0040] Substituting equation (1) into equation (2) yields

[0041] (3)

[0042] From equation (3), we can obtain

[0043] (4)

[0044] because

[0045] (5)

[0046] Combining equations (4) and (5) yields

[0047] (6)

[0048] From equation (6), it can be seen that we only need to find U 1 / 4rms By combining Sinδ and Cosδ, we can obtain U. rms Sinδ and Cosδ can be calculated in real time by the phase-locked loop. 1 / 4rms It can be obtained from equation (7):

[0049] (7).

Claims

1. A voltage sag detection method that balances speed and anti-interference capability, characterized in that: The voltage amplitude Urms is calculated using the voltage of a 1 / 4 cycle, and the calculated voltage amplitude is repeatedly judged to determine whether it belongs to the low voltage condition of the system. The amplitude Urms of the system voltage is calculated by obtaining the root mean square value U1 / 4rms of the 1 / 4 cycle and the sinδ and cosδ of the phase angle δ. The sinδ and cosδ can be obtained in real time by the phase-locked loop. Assume the single-phase voltage is （1） Among them, U rms This represents the effective value of the voltage period. According to the definition of the effective value of a continuous periodic signal, the root mean square value of the voltage during a quarter cycle can be expressed as: （2） Among them, U 1 / 4rms The effective value of the voltage is 1 / 4 cycle, and δ is from 0 to... Any value between; Substituting equation (1) into equation (2) yields （3） From equation (3), we can obtain （4） because （5） Combining equations (4) and (5) yields （6） From equation (6), it can be seen that we only need to find U 1 / 4rms By combining Sinδ and Cosδ, we can obtain U. rms Sinδ and Cosδ can be calculated in real time by the phase-locked loop. 1 / 4rms It can be obtained from equation (7) （7）。 2. The voltage sag detection method that balances speed and anti-interference capability according to claim 1, characterized in that: The effective value Urms of the system voltage is calculated.

3. The voltage sag detection method that balances speed and anti-interference capability according to claim 1, characterized in that: The amplitude of the system voltage is calculated using a 1 / 4 cycle sliding window.

4. The voltage sag detection method that balances speed and anti-interference capability according to claim 1, characterized in that: The delay is 2ms when used to detect the 90% voltage sag commonly used in engineering practice.

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