A photovoltaic power station direct current boost converter bus capacitor aging fault early warning method

Abstract

The application discloses a kind of photovoltaic power station direct-current boost converter bus capacitor aging failure early warning method, obtains the voltage on public direct-current bus u b And current on direct-current cable i O ; determine the zero-crossing time of current i O t n ; calculate N ( N -1) / 2 group results;Determine the zero-crossing point of area formed by current i O and time axis t′ q ; calculate three variables at t=tm;Calculate Q -1 group results;Calculate the point in three-dimensional space;According to least square method fitting plane, determine ω 1、 ω 2 and ω 3;Obtain R x and C x ; calculate D and D 0 ratio;When D and D 0 ratio is greater than set threshold α, then determine that bus capacitor has failed;Otherwise, determine that bus capacitor has not failed.The application can effectively avoid the influence of direct-current cable parameter change, realize direct-current boost converter bus capacitor aging failure timely determination and early warning.​

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power plant equipment monitoring and operation and maintenance, specifically to a method for early warning of aging faults in the bus capacitors of a DC boost converter in a photovoltaic power plant. Background Technology

[0002] In photovoltaic (PV) power plants, DC-DC boost converters play a crucial role. By converting the low-voltage DC power generated by PV modules into higher-voltage DC power, they integrate maximum power point tracking (MPPT) technology to ensure maximum energy capture and conversion efficiency. Their internal bus capacitors smooth the output voltage, reduce voltage fluctuations, and provide instantaneous power compensation. However, bus capacitors are prone to failure, including overheating, voltage breakdown, and excessive ripple current. These failures are typically caused by the drying out of the electrolyte and dielectric degradation during long-term operation, leading to a decrease in capacitance and ultimately, failure. Regular inspection and maintenance are usually required to ensure the safe operation of the PV power plant.

[0003] The aging condition of the bus capacitors in a DC-DC boost converter can be determined by their equivalent series resistance ( R x ) and equivalent series capacitance ( C x Quantification. Typically, R x Double or C x A 20% reduction indicates that the bus capacitor has experienced aging and failure. However, considering the limitations of sensors installed in actual photovoltaic power plants—namely, the current on the DC-DC boost converter bus capacitor is unknown, and only the output current of the DC-DC boost converter can be obtained; and the fluctuations in the photovoltaic array's power generation cause the voltage on the DC bus capacitor to be not a standard DC current, but a quasi-DC current—this limits the application and implementation of many existing methods.

[0004] To address the above engineering realities, it is necessary to utilize the electrical quantities measured by sensors already installed on-site to obtain the equivalent electrical parameters of the DC-DC boost converter bus capacitors. R x and C x This paper proposes an accurate estimation method for aging fault judgment and a highly sensitive aging fault judgment index to achieve timely judgment and early warning of aging faults in the bus capacitors of DC-DC boost converters. Currently, the invention patent "Online Diagnostic Method for DC Bus Capacitors of Photovoltaic System DC-DC Converters" (application number: CN202310124370.5) proposes a method for estimating the equivalent electrical parameters of the bus capacitors. C x The estimation method, when C xThe estimated value is reduced to 80% of the initial value, and a fault protection signal is sent. However, the method (1) proposed in this patent can only estimate C x But can not estimate R x ; (2) C x The estimation accuracy is not high, and is affected by the change of the DC cable parameters; (3) due to the inability to obtain R x , the aging state diagnosis sensitivity is insufficient, and a sensitive aging index is lacking to play a timely fault warning role. SUMMARY

[0005] In view of the defects in the prior art, the present application provides a photovoltaic power station DC booster converter bus capacitor aging fault warning method. The electrical quantities measured by the sensors installed on site, i.e. the voltage u b and the current i O on the DC cable, are used to accurately estimate the equivalent electrical parameters R x and C x of the DC booster converter bus capacitor, and the change trend of R x and C x is combined to propose a high-sensitivity aging fault judgment index D , effectively avoiding the influence of the change of the DC cable parameters, realizing the timely judgment and warning of the aging fault of the DC booster converter bus capacitor.

[0006] The technical scheme adopted by the present application is: a photovoltaic power station DC booster converter bus capacitor aging fault warning method, the method comprising the following steps:

[0007] Step 1: obtain the voltage u b on the common DC bus and the current i O on the DC cable;

[0008] Step 2: determine the zero-crossing time i O of the current t n ;

[0009] Step 3: calculate N ( N -1) / 2 groups of results, i.e. ;

[0010] Step 4: Determine the current i O The area formed by the time axis and the zero-crossing point ;

[0011] Calculate the three variables at t = tm, namely ;

[0012] Step 5: Calculate Q -1 group of results, namely ;

[0013] Step 6: Calculate , get the point in the three-dimensional space and ;

[0014] Step 7: According to the least square method to fit the plane , determine and ;

[0015] Step 8: Obtain R x and C x ;

[0016] Step 9: Calculate the aging evaluation index D ;

[0017] Step 10: Calculate D and D 0 ratio; when D and D 0 ratio is greater than the set threshold α, it is determined that the bus capacitor has failed; otherwise, it is determined that the bus capacitor has not failed.

[0018] Further, in step 1, the common DC bus voltage u b and the current on the DC cable i O has the following relationship:

[0019] ;

[0020] Wherein, l 0 is the equivalent inductance parameter of the DC cable as a whole.

[0021] Further, in step 2, specifically comprising, according to formula (1), record i O The zero-crossing point is t n , that is i O ( t n) =0, wherein 1≤ n n + x ≤ N。

[0022] Further, the step 3 specifically comprises obtaining the calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2). N t n Further, the step 4 specifically comprises obtaining the calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2). N ( N -1) / 2 groups of calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2). u b Further, the step 5 specifically comprises obtaining the calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2). i O Further, the step 6 specifically comprises obtaining the calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2).

[0023] ;

[0024] wherein, t is the time point, V is the voltage, I is the current, and t0 is the time point corresponding to the voltage and current measurement results. .

[0025] Further, the step 4, specifically comprises obtaining the calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2). i O Further, the step 5, specifically comprises obtaining the calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2). , wherein t is the time point, V is the voltage, I is the current, and t0 is the time point corresponding to the voltage and current measurement results. . .

[0026] Further, the step 6, specifically comprises obtaining the calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2). Q Further, the step 7, specifically comprises fitting a three-dimensional plane P using the least square method. Q u b Further, the step 8, specifically comprises fitting a three-dimensional plane P using the least square method. i O Further, the step 9, specifically comprises fitting a three-dimensional plane P using the least square method.

[0027] .

[0028] Further, the step 6, specifically comprises obtaining the calculation results of the voltage and current of the time point t according to the formula (1) and the formula (2). , obtaining the points P1 and P2 in the three-dimensional space. Further, the step 7, specifically comprises fitting a three-dimensional plane P using the least square method.

[0029] Further, the step 8, specifically comprises fitting a three-dimensional plane P using the least square method. ; the three-dimensional plane has the following expression

[0030] ;

[0031] wherein, P is the three-dimensional plane column vector, and a, b, and c are the three-dimensional plane column vector. ω 1, ω 2 and ω ​​​​​​3 is a three-dimensional plane coefficient, and l 0, C x and R x has the following relationship

[0032] ;

[0033] Therefore, according to the three-dimensional plane expression obtained by fitting, the values of ω 1, ω 2 and ω 3 are obtained;

[0034] The step 8 is to calculate R x and C x .

[0035] Further, the step 9 specifically includes defining an aging failure judgment index D , which has the following expression

[0036] ;

[0037] Since in the conventional photovoltaic power station, l 0 is of the order of 10 -5 ~10 -3 , l 0 is of the order of 10 -10 ~10 -6 ; therefore l 0 squared is much smaller than the value 1, so

[0038] ;

[0039] According to formula (7), D it is considered to be independent of the DC cable parameters, so the aging state diagnosis result will not be affected by the change of the DC cable parameters.

[0040] Further, the step 9 specifically includes defining the output side bus capacitor health aging evaluation index as D 0;

[0041] When the ratio of D to D 0 is greater than a set threshold α, it is determined that the bus capacitor is about to fail, that is

[0042] .

[0043] Beneficial technical effects:

[0044] The application provides a photovoltaic power station DC boost converter bus capacitor aging fault early warning method, which utilizes the electrical quantity measured by the installed sensor on site, i.e. u b and the current on the DC cable i O , realizes accurate estimation of equivalent electrical parameters of the DC boost converter bus capacitor R x and C x , and combines the change trends of R x and C x , proposes a high-sensitivity aging fault judgment index D , effectively avoids the influence of the change of the DC cable parameters, realizes timely judgment and early warning of the aging fault of the DC boost converter bus capacitor. BRIEF DESCRIPTION OF DRAWINGS

[0045] The application has the following drawings:

[0046] Figure 1 A typical topology diagram of a photovoltaic power station

[0047] Figure 2 An equivalent circuit diagram of a boost DC converter and a DC cable

[0048] Figure 3 An equivalent circuit diagram of an output side bus capacitor

[0049] Figure 4 A schematic diagram

[0050] Figure 5 A schematic diagram

[0051] Figure 6 and Distribution diagrams and fitting three-dimensional plane schematic diagrams

[0052] Figure 7 u b and i O A schematic diagram

[0053] Figure 8 Distribution diagrams and fitting three-dimensional plane schematic diagrams of five groups of bus capacitors under aging states and DETAILED DESCRIPTION

[0054] ​For the above purposes, features and advantages of the present application to be more clearly and easily understood, the following will combine the accompanying drawings Figures 1-8 and specific embodiments to make a further detailed description of the present application.

[0055] The present application is a kind of photovoltaic power station DC boost converter bus capacitor aging fault early warning method, comprising the following principles and steps:

[0056] Figure 1 For photovoltaic power station typical topology, including photovoltaic cell panel, DC boost converter, DC cable, public DC bus, inverter and three-phase power grid. According to Figure 2 , the patent research object is the output side bus capacitor in DC boost converter. According to Figure 3 , the output side bus capacitor can be equivalent to equivalent resistance R x And equivalent capacitance C x During the aging process of bus capacitor, R x Trend, C x Trend.

[0057] In the process of photovoltaic power station operation, DC boost converter will automatically exit when the light intensity weakens every day. When the DC boost converter automatically exits (i.e. according to Figure 4 , t = t 0), the public DC bus voltage u b And the current on the DC cable i O Has the following relationship:

[0058] ;

[0059] Among them, l 0 is the equivalent inductance parameter of the whole DC cable,

[0060] According to Figure 4 , let i O The zero crossing moment is t n , that is i O ( t n ) =0, where 1≤ n < n + x ≤ N . According to N , the number of t nThe voltage and current measurement results at the corresponding time can be obtained. N ( N -1) / 2 group related u b and i O The calculation result, i.e.

[0061] ;

[0062] in, .

[0063] according to Figure 5 ,remember i O The moment when the area enclosed by the time axis equals 0 is... ,Right now ,in .according to Q indivual The voltage and current measurement results at the corresponding time can be obtained. Q -1 group related u b and i O The calculation result, i.e.

[0064] ;

[0065] make This allows us to obtain several points in three-dimensional space. and ,like Figure 6 As shown. Among them, represent , represent Based on these points, a three-dimensional plane is fitted using the least squares method. The three-dimensional plane has the following expression.

[0066] ;

[0067] in, It is a three-dimensional planar column vector. ω 1, ω 2 and ω 3 is the three-dimensional plane coefficient, and... l 0, C x and R x It has the following relationship

[0068] ;

[0069] Therefore, the three-dimensional plane expression obtained by fitting can be used to obtain ω 1, ω 2 and ω 3, and then calculate R x and C x .

[0070] An aging fault judgment index is defined D , which has the following expression

[0071] ;

[0072] Since in a conventional photovoltaic power station, l 0 is of the order of 10 -5 ~10 -3 , therefore l 0 squared is much smaller than the value 1, so

[0073] ;

[0074] According to equation (7), D it is considered to be independent of the DC cable parameters, so the aging state diagnosis result will not be affected by the change of the DC cable parameters.

[0075] The aging evaluation index of the output side bus capacitor health is defined as D 0. When D and D 0 ratio is greater than the set threshold α, it is determined that the bus capacitor is about to fail, that is

[0076] ;

[0077] Application example:

[0078] As shown in Figure 7 and Figure 8 , a photovoltaic power station model is built in the simulation software MATLAB / Simulink. In the simulation model, the parameters are set, the DC cable parameters l 0=2 10 -4 H, and in the gradual aging process, the output side bus capacitor R x increases, C x decreases. Five groups of bus capacitor aging states are set, and the simulation parameters in the model are:

[0079] G-I: R x =32 mΩ and C x =2.5 mF;

[0080] G-II: R x = 40 mΩ and C x = 2.375 mF;

[0081] G-III: R x = 48 mΩ and C x = 2.25 mF;

[0082] G-IV: R x = 56 mΩ and C x = 2.125 mF;

[0083] G-V: R x = 64 mΩ and C x = 2.0 mF R 1 time compared to healthy value; C x 20% less

[0084] In the simulation model, at 0.3 s, the DC boost converter exits. When the health bus capacitor is healthy, the voltage on the common DC bus u b and the current on the DC cable i O as shown in Figure 1

[0085] Take h = 1000, α = 1.2.

[0086] According to the implementation steps, the calculation results of ω 1, ω 2 and ω 3 and R x , C x are as follows:

[0087]

[0088] According to the above results, R x and C x The calculation results match the parameters set in the model. In G-I, G-II, G-III, G-IV, D / D 0 is less than 1.2, and in G-V, D / D ​​0 is greater than 1.2, it is determined that the bus capacitor of the group has developed an aging fault.

[0089] The above embodiments have described the technical solutions of the present application in detail. Apparently, the present application is not limited to the described embodiments. Based on the embodiments in the present application, those skilled in the art can make various changes, but any change equivalent or similar to the present application falls within the protection scope of the present application. The contents not described in detail in the specification belong to the prior art known to those skilled in the art.

Claims

1. A photovoltaic power station DC boost converter bus capacitor aging fault early warning method, characterized in that, The method comprises the following steps: Step 1 : Obtain the voltage on the common DC bus u b and the current on the DC cable i O ; Step 2: Determine current i O Time of zero crossing t n ; Step 3: Calculation N ( N -1) / 2 groups of results, i.e. ; Step 4: Determine the current i O Area formed with the time axis zero crossing ; The three variables at time t = t m are computed, i.e. ; Step 5: Calculation Q -1 group results, i.e. ; Step 6: Calculate , to get the point in three-dimensional space and ; Step 7: Fit a plane according to least squares method , determine ω 1, ω 2 and ω 3; Step 8: Obtain R x and C x ; Step 9: Calculate the aging assessment index D ; Step 10: Calculation D With D 0 ratio; When D With D 0 ratio is greater than a set threshold a, then it is determined that the bus capacitor has failed; otherwise it is determined that the bus capacitor has not failed; Step 3 specifically includes, according to N indivual t n The voltage and current measurement results at the corresponding time are obtained. N ( N -1) / 2 group related u b and i O The calculation result, i.e. ; wherein ; The step 5 specifically includes obtaining the voltage and current measurement results corresponding to the time point according to Q One The voltage and current measurement results corresponding to the time point are obtained Q -1 group of relevant u b And i O The calculation results, namely ； The step 9 specifically includes defining an aging failure judgment index D with the following expression ; Since in conventional photovoltaic power stations, l 0 is of the order of magnitude of , l 0 is of the order of magnitude of ; Therefore l 0 is much smaller than the value 1, then ; According to equation (7), D It is considered that the aging state diagnosis result is not affected by the change of the DC cable parameter regardless of the DC cable parameter.

2. The photovoltaic power station DC boost converter bus capacitor aging fault early warning method of claim 1, characterized in that, In said step 1, the common DC bus voltage u b and the current on the DC cable i O has the following relationship: ; wherein l 0 is the equivalent inductance parameter of the overall DC cable.

3. The photovoltaic power station DC boost converter bus capacitor aging fault early warning method of claim 2, characterized in that, The step 2 specifically includes, according to formula (1), recording i O The zero-crossing time is t n That is i O ( t n ) =0, where 1≤ n < n + x ≤ N。 4. The photovoltaic power station DC boost converter bus capacitor aging fault early warning method of claim 3, characterized in that, The step 4 specifically includes, according to formula (1), recording i O The area formed by the time axis is equal to 0 at the moment That is Wherein .

5. The photovoltaic power station DC boost converter bus capacitor aging fault early warning method of claim 4, wherein, The step 6 specifically includes , obtaining a point in three-dimensional space and .

6. The photovoltaic power station DC boost converter bus capacitor aging fault early warning method of claim 5, wherein, The step 7 specifically comprises fitting a three-dimensional plane by using a least square method The three-dimensional plane has the following expression ; wherein is a three-dimensional planar column vector, ω 1, ω 2 and ω 3 are three-dimensional planar coefficients, and l 0, C x and R x have the following relationship ; Thus, from the three-dimensional plane expression obtained by fitting, we obtain ω 1, ω 2 and ω 3; The step 8 is to calculate according to formula (5) R x and C x .

7. The photovoltaic power station DC boost converter bus capacitor aging fault early warning method of claim 6, wherein, The step 9 specifically includes defining the aging evaluation index of the output side bus capacitor health as D 0; When D With D 0 ratio is greater than a set threshold α, then it is determined that the bus capacitor is about to fail, that is 。

Images