A three-phase unbalance degree evaluation method based on local real-time information of grid-connected point

Abstract

This invention proposes a three-phase imbalance assessment method based on real-time local information from the grid connection point. This method improves the timeliness and accuracy of three-phase imbalance assessment by collecting real-time local information from the grid connection point, separating positive, negative, and zero-sequence real-time values, calculating the average values ​​of positive, negative, and zero-sequence values, and calculating the negative-sequence imbalance degree and the zero-sequence imbalance degree. It solves the technical problem of three-phase power imbalance, eliminates the dependence on the head-end transformer and long-distance communication, and allows for more flexible installation of three-phase power balance equipment. This facilitates distributed resolution of three-phase power imbalance, improves power quality and supply efficiency, and has the advantages of high efficiency, speed, and low cost. It solves the problem of delayed or inaccurate three-phase balance assessment caused by untimely or inaccurate assessment of three-phase imbalance in traditional power systems. Therefore, it is suitable for application as a three-phase imbalance assessment method based on real-time local information from the grid connection point.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and more specifically, to a method for assessing three-phase imbalance based on local real-time information from the grid connection point. Background Technology

[0002] With numerous single-phase distributed power sources and high-power single-phase loads randomly connected to the power grid, the phenomenon of three-phase imbalance in the power grid is becoming increasingly significant. Three-phase imbalance not only increases energy losses in lines or distribution transformers, leading to energy waste and affecting the operating efficiency of motors, but it can also cause a decrease in the output of distribution transformers. When a distribution transformer operates under unbalanced three-phase load conditions, its output capacity is unlikely to reach its rated value, its reserve capacity will also be reduced, and its overload capacity will also decrease. If a distribution transformer operates under overload conditions, it is very easy for the transformer to overheat, and in severe cases, it may even burn out the transformer equipment.

[0003] Three-phase imbalance in the power grid can also generate zero-sequence current in the distribution transformer. When this zero-sequence current passes through steel components, it will cause eddy current losses and hysteresis, leading to localized overheating of the steel components. The winding insulation of the distribution transformer may also age faster due to overheating, resulting in a reduced equipment lifespan. At the same time, the presence of zero-sequence current will also increase the losses of the distribution transformer.

[0004] When power is supplied under three-phase imbalance, the electrical equipment connected to the high-voltage phase is prone to burnout, while the electrical equipment connected to the low-voltage phase may not be able to be used normally, posing a serious threat to the safe operation of the electrical equipment.

[0005] Therefore, accurate assessment of three-phase imbalance is of great significance for improving power grid operating efficiency and reducing energy waste. However, in current power systems, there are few methods for assessing three-phase imbalance. These methods typically require multi-point sampling and historical information for calculation, resulting in complex algorithms, high hardware costs, and poor real-time performance.

[0006] Existing methods for assessing three-phase imbalance typically involve directly comparing the three-phase power information collected from the transformer at the beginning of the line. However, equipment for handling three-phase imbalance may not be installed at the beginning of the line, leading to long-distance communication issues. This can result in untimely or inaccurate assessment of three-phase imbalance, causing delays or inaccuracies in three-phase balance, reducing power quality, increasing transformer copper losses, and thus reducing power transmission efficiency.

[0007] Therefore, there is an urgent need to study a method that can effectively assess the three-phase imbalance of the power grid by combining local real-time information. Summary of the Invention

[0008] To accurately and effectively assess three-phase imbalance, this invention proposes a three-phase imbalance assessment method based on local real-time information from the grid connection point. This method improves the timeliness and accuracy of three-phase imbalance assessment by collecting local real-time information from the grid connection point, separating positive, negative, and zero-sequence real-time values, calculating the average values ​​of positive, negative, and zero-sequence values, and calculating the negative-sequence imbalance and zero-sequence imbalance. It solves the technical problem of three-phase power imbalance and is suitable for application as a three-phase imbalance assessment method.

[0009] The solution adopted by this invention to solve the technical problem is: A three-phase imbalance assessment method based on real-time local information at the grid connection point is implemented through the following steps: Step 1: Collect the real-time value of the three-phase voltage of the grid-connected node. The sampling frequency should be no less than 1kHz.

[0010] Step 2: Calculate the real-time value of the zero-sequence component, and calculate the real-time value of the three-phase voltage after removing the zero-sequence component.

[0011] Step 3: Separate the positive and negative sequence components to obtain the real-time values ​​of the three-phase positive sequence components and the three-phase negative sequence components.

[0012] Step 4: Calculate the average value of the positive and negative zero components respectively.

[0013] Step 5: Calculate the negative order imbalance and the zero order imbalance respectively.

[0014] The technical effects and advantages of this invention are as follows: This invention uses grid information to assess three-phase power imbalance, eliminating the reliance on the head-end transformer and long-distance communication. This makes the installation location of the three-phase power balance equipment more flexible, which is conducive to distributed solutions for three-phase power imbalance and improves power quality and power supply efficiency.

[0015] The method described in this invention assesses three-phase imbalance solely based on real-time information from the grid connection point, offering advantages such as high efficiency, speed, and low cost. It solves the problem of delayed or inaccurate three-phase balance assessments in traditional power systems, which often result from untimely or inaccurate evaluations. Therefore, it is suitable as a three-phase imbalance assessment method based on real-time information from the grid connection point. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0018] A three-phase imbalance assessment method based on real-time local information at the grid connection point is implemented through the following steps: Step 1: Collect real-time values ​​of the three-phase voltage at the grid-connected nodes. (Calculation / Operation) u a , u b , u c Sampling frequency meter f s The frequency requirement is no less than 1kHz.

[0019] Step 2: Calculate the real-time value of the zero-sequence component. Using... u 0 represents the real-time value of the zero-sequence component. The real-time values ​​of the three-phase voltages after removing the zero-sequence component are calculated, and these real-time values ​​are represented by... u ' a , u ' b , u ' c express.

[0020] The specific calculation method for step 2 is as follows: Real-time value of zero-sequence component u 0, calculate as follows:

[0021] Real-time values ​​of three-phase voltages after removing zero-sequence components u ' a , u ' b , u ' c Perform the calculation as follows.

[0022]

[0023] Step 3: Separate the positive and negative sequence components. Obtain the real-time values ​​of the three-phase positive sequence components. u + a , u + b , u + c Real-time value of three-phase negative sequence component u - a , u - b , u - c .

[0024] The specific calculation method for step 3 is as follows: First, the real-time three-phase voltage values, after removing the zero-sequence component, are projected onto...αβ On the axis, obtain the following formulas respectively. αβ Real-time components on the axis u α , u β

[0025] Then αβ The on-axis processes the real-time signals to obtain their respective real-time values ​​delayed by 1 / 4 period. u’ α , u’ β Define the power grid frequency as... f n Under normal circumstances f n =50Hz:

[0026] Then, through calculation, the positive and negative order components are obtained respectively. αβ Axial projection. Positive sequence components in αβ The projections of the axes are calculated respectively. u + α , u + β .

[0027]

[0028] Negative order components in αβ The projections of the axes are calculated respectively. u - α , u - β .

[0029]

[0030] Finally, the real-time values ​​of the three-phase positive and negative sequence components were obtained, and the real-time value of the positive sequence component was obtained. u + a , u + b , u + c .

[0031]

[0032] Real-time value of three-phase negative sequence component u -a , u - b , u - c .

[0033]

[0034] Step 4: Calculate the average values ​​of the positive and negative zero components respectively, expressed as follows: U + , U - , U 0 The specific calculation method for step 4 is as follows: First, calculate the number of samples per power frequency cycle. N , N = f s / f n .

[0035] Then calculate the average values ​​for the positive, negative, and zero sequences respectively. U + , U - , U 0

[0036] in, Indicates N consecutive times u + a The real-time sampling results are all cumulative sums of the values. Since the positive and negative sequence three-phase components are completely symmetrical, the result remains unchanged when using the real-time value of any one of the components.

[0037] Step 5: Calculate the negative order imbalance degree separately. e 2 and zero-sequence imbalance e 0.

[0038] The specific calculation method for step 5 is as follows: Negative order balance e 2 and zero-sequence balance e 0 is defined as the ratio of the effective value of the negative-order component, the effective value of the zero-order component, and the effective value of the positive-order component, respectively. Considering that the effective value and the average are proportional, the calculation is simplified here, and the negative-order balance degree is obtained directly according to the following formula. e 2 and zero-sequence balance e 0.

[0039]

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for evaluating three-phase unbalance degree based on local real-time information of a point of common coupling, characterized in that, Includes the following steps: Step 1: Collect the real-time values ​​of the three-phase voltage at the grid-connected node, with a sampling frequency of not less than 1kHz; Step 2: Calculate the real-time value of the zero-sequence component, and calculate the real-time value of the three-phase voltage after removing the zero-sequence component; Step 3: Separate the positive and negative sequence components to obtain the real-time values ​​of the three-phase positive sequence components and the three-phase negative sequence components; Step 4: Calculate the average value of the positive and negative zero components respectively; Step 5: Calculate the negative order imbalance and the zero order imbalance respectively.

2. The three-phase imbalance assessment method based on local real-time information at the grid connection point as described in claim 1, characterized in that: The real-time value of the three-phase voltage in step 1 is denoted as u a , u b , u c The sampling frequency is denoted as f s , and is required to be no less than 1 kHz.

3. The three-phase imbalance assessment method based on local real-time information at the grid connection point according to claim 2, characterized in that: In step 2, when calculating the real-time value of the zero-sequence component, the following is used: u 0 represents the real-time value of the zero-sequence component, and the real-time value of the three-phase voltage after removing the zero-sequence component is calculated. u ' a , u ' b , u ' c The specific calculation method is as follows: Real-time value of zero-sequence component u 0, calculate as follows: ； Real-time values ​​of three-phase voltages after removing zero-sequence components u ' a , u ' b , u ' c Calculate using the following method: 。 4. The three-phase imbalance assessment method based on local real-time information at the grid connection point as described in claim 3, characterized in that: In step 3, which separates the positive and negative sequence components, the real-time value of the three-phase positive sequence component is... u + a , u + b , u + c The real-time value of the three-phase negative sequence component is u - a , u - b , u - c , The specific calculation method is as follows: First, the real-time three-phase voltage values, after removing the zero-sequence component, are projected onto... αβ On the axis, obtain the following formulas respectively. αβ Real-time components on the axis u α , u β ； Then αβ The real-time signals are processed on the axis to obtain their respective real-time values ​​delayed by 1 / 4 period. u’ α , u’ β Define the power grid frequency as f n Under normal circumstances f n =50Hz: ； Then, through calculation, the positive and negative order components are obtained respectively. αβ Axis projection, positive sequence component in αβ The projections of the axes are calculated respectively. u + α , u + β , ； Negative order components in αβ The projections of the axes are calculated respectively. u - α , u - β , ； Finally, the real-time values ​​of the three-phase positive and negative sequence components were obtained, and the real-time value of the positive sequence component was obtained. u + a , u + b , u + c , ； Real-time value of three-phase negative sequence component u - a , u - b , u - c , 。 5. The three-phase imbalance assessment method based on local real-time information at the grid connection point as described in claim 4, characterized in that: In step 4, the average values ​​of the positive and negative zero components are expressed as follows: U + , U - , U 0, The specific calculation method is as follows: First, calculate the number of sampling points for each power frequency cycle. N , N = f s / f n , Then calculate the average values ​​for the positive and negative zero sequences respectively. U + , U - , U 0, ； in, Indicates N consecutive times u + a The real-time sampling results are all cumulative sums of values. Since the positive and negative sequence three-phase components are completely symmetrical, the result remains unchanged when using the real-time value of any one of the terms.

6. The three-phase imbalance assessment method based on local real-time information at the grid connection point according to claim 5, characterized in that: In step 5, the negative order imbalance degree is: ε 2. Zero-sequence imbalance is ε 0, the specific calculation method is as follows: Negative order balance ε 2 and zero-sequence balance ε 0 is defined as the ratio of the effective value of the negative-order component, the effective value of the zero-order component, and the effective value of the positive-order component, respectively. Considering that the effective value and the average are proportional, the negative-order balance degree is calculated according to the following formula. ε 2 and zero-sequence balance ε 0， 。

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