A method for indirect measurement of system impedance based on low voltage fault generation device

Abstract

The present invention discloses a method for indirectly measuring system impedance based on a low voltage fault generating device, wherein a low voltage fault generating device is used to perform a no-load test, and the no-load test data is used to list the system impedance Z. sx The resistance R sx and inductor X sx Solve the quadratic equations with two unknown variables to get the resistance R sx and inductor X sx value, and finally obtain the system impedance Z sx ; In view of the fact that there is a certain deviation between the measured value and the true value, in order to improve the accuracy of the system impedance, multiple no-load tests are carried out for different test conditions, and the equation groups are listed in pairs to solve the system impedance under each test condition. The system impedance is averaged to obtain a more accurate system impedance value. Based on the system impedance value, the low-voltage fault generating device can efficiently and accurately select the current limiting impedance and short-circuit impedance, accurately control the voltage drop amplitude and phase jump, and reduce the damage of high voltage to the wind turbine and converter.

Description

Technical Field

[0001] The present invention relates to the technical field of low voltage ride-through capability testing of wind turbine generator sets, and in particular to a method for indirectly measuring system impedance based on a low voltage fault generating device. Background Art

[0002] Fault voltage ride-through capability refers to the ability of a wind turbine or photovoltaic power generation system to continue operating and support grid recovery when the grid voltage drops or rises to a certain value. As a necessary condition for the integration of new energy sources into the grid, new energy power plants must conduct fault voltage ride-through capability testing and meet testing requirements. When conducting fault voltage ride-through capability tests, system impedance is one of the key factors affecting voltage changes and phase jumps. Quickly and accurately obtaining the actual system impedance value at the test site is of great practical significance for fault voltage ride-through capability testing. Based on the accurate system impedance value, the fault voltage generator can efficiently and accurately select the current limiting impedance and short-circuit impedance, precisely control the voltage drop amplitude and phase jump, and reduce the damage caused by high voltage to wind turbines and converters. Summary of the Invention

[0003] The purpose of the present invention is to address the deficiencies in the prior art and provide a method for indirectly measuring system impedance based on a low-voltage fault generating device. A no-load test is performed using the low-voltage fault generating device, and the resistance and inductance values of the system impedance are obtained based on the no-load test data. In order to improve the accuracy of the system impedance, multiple no-load tests are performed for different test conditions, and the system impedance is averaged.

[0004] To achieve the above objectives, the present invention provides a technical solution: a method for indirectly measuring system impedance based on a low voltage fault generating device, wherein the low voltage fault generating device is connected in series to the high voltage side of the wind turbine step-up transformer, and the method comprises the following steps:

[0005] S1. Perform multiple no-load tests using a low-voltage fault generator for different test conditions to obtain multiple sets of no-load test data corresponding to different test conditions.

[0006] S2. Based on each set of no-load test data, calculate and obtain multiple system impedances corresponding to different test conditions and the resistance and inductance values corresponding to each system impedance;

[0007] S3. Calculate the average resistance and inductance values based on the resistance and inductance values corresponding to each system impedance, and ultimately determine the system impedance of the access point between the low-voltage fault generating device and the high-voltage side of the wind turbine step-up transformer, thereby controlling the voltage drop amplitude and phase jump during the low-voltage ride-through capability test of the wind turbine fault.

[0008] Furthermore, the low voltage fault generating device is electrically connected to the external power grid, which includes a system impedance Z in series. sx , current limiting impedance Z sr and short-circuit impedance Z sc The current limiting impedance Zsr is used to limit the impact of the fault voltage on the power grid and other wind turbines in the wind farm. The calculation formula is:

[0009] Z sr =R sr +jX sr ,

[0010] Among them, R sr The resistor of the current limiting impedance, X sr is the inductor of the current-limiting impedance;

[0011] The short-circuit impedance Z sc The voltage drop required for the test is generated at the access point and is calculated as follows:

[0012] Z sc =R sc +jX sc ,

[0013] Among them, R sc is the resistance of the short-circuit impedance, X sc The inductance is the short-circuit impedance;

[0014] The system impedance Z sx The calculation formula is:

[0015] Z sx =R sx +jX sx ,

[0016] Among them, R sx is the resistance of the system impedance, X sx The inductance is the system impedance.

[0017] Furthermore, in step S1, the following operations are specifically performed:

[0018] Under each test condition, two no-load tests with different voltage drop amplitudes were performed using a low-voltage fault generating device. That is, under the premise of the same system impedance and two different voltage drop amplitudes, two different sets of current limiting impedances and short-circuit impedances were calculated, which are a set of no-load test data under the corresponding test condition.

[0019] Furthermore, in step S2, the following operations are specifically performed:

[0020] The equation group is established based on each group of no-load test data obtained:

[0021]

[0022] Where n is a positive number, representing the total number of test conditions; U d is the voltage drop amplitude; R sr The resistor of the current limiting impedance, X sr is the inductor of the current limiting impedance; R sc is the resistance of the short-circuit impedance, X sc is the inductance of the short-circuit impedance; R sx is the resistance of the system impedance, X sx The inductance is the system impedance;

[0023] According to the above equations, the resistance of the system impedance corresponding to all test conditions is {R sx1 ,R sx2 ,...,R sxn}, the inductance of the system impedance corresponding to all test conditions is {X sx1 ,X sx2 ,...,X sxn}.

[0024] Furthermore, in step S3, the following operations are specifically performed:

[0025] According to the resistance value {R sx1 ,R sx2 ,...,R sxn} and the inductance {X sx1 ,X sx2 ,...,X sxn}, calculate the average resistance R and the average inductance X:

[0026]

[0027]

[0028] Where i is a positive number; n is a positive number representing the total number of test conditions;

[0029] Finally determine the system impedance Z of the connection point between the low voltage fault generating device and the high voltage side of the wind turbine step-up transformer:

[0030] Z=R+jX.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] The present invention can improve the accuracy of system impedance. In the low voltage ride-through capability test of a wind turbine fault, the current limiting impedance and short-circuit impedance can be selected efficiently and accurately based on a more accurate system impedance, and the voltage drop amplitude and phase jump can be precisely controlled to reduce the damage of high voltage to the wind turbine and converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a structural diagram of a low voltage fault generating device.

[0034] Figure 2 This is the equivalent circuit diagram of the low voltage fault generating device. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific embodiments.

[0036] See also Figures 1 to 2 As shown, the low voltage fault generating device provided by this embodiment is connected in series to the high voltage side of the wind turbine step-up transformer 2, and the low voltage fault generating device is electrically connected to the external power grid 1, which includes a system impedance Z in series. sx , current limiting impedance Z sr and short-circuit impedance Z sc The current limiting impedance Zsr is used to limit the impact of the fault voltage on the power grid and other wind turbines in the wind farm. The calculation formula is:

[0037] Z sr =R sr +jX sr ,

[0038] Among them, R sr The resistor of the current limiting impedance, X sr is the inductor of the current-limiting impedance;

[0039] The short-circuit impedance Z sc For access point U TP The voltage drop required for the test is calculated as follows:

[0040] Z sc =R sc +jX sc ,

[0041] Among them, R sc is the resistance of the short-circuit impedance, X sc For the inductor of the short-circuit impedance, closing the short-circuit switch CB2 connects the three or two phases of the short-circuit impedance together, generating the voltage drop amplitude required by the test at the test point;

[0042] The system impedance Z sx The calculation formula is:

[0043] Z sx =R sx +jX sx ,

[0044] Among them, R sx is the resistance of the system impedance, X sxThe inductance is the system impedance;

[0045]

[0046]

[0047]

[0048]

[0049] in, is the grid voltage; is the system impedance voltage; is the current limiting impedance voltage; is the short-circuit impedance voltage; is the grid current; U d is the voltage drop amplitude.

[0050] The method for indirectly measuring system impedance based on a low voltage fault generating device includes the following steps:

[0051] S1. For different test conditions, use the low voltage fault generating device to perform multiple no-load tests to obtain multiple sets of no-load test data corresponding to different test conditions. Specifically, perform the following operations:

[0052] Under each test condition, two no-load tests with different voltage drop amplitudes were performed using a low-voltage fault generator. That is, under the premise of the same system impedance and two different voltage drop amplitudes, two different sets of current limiting impedances and short-circuit impedances were calculated. This is a set of no-load test data under the corresponding test condition, as shown in the following table:

[0053] System impedance Current limiting impedance Short-circuit impedance Voltage drop amplitude <![CDATA[Z sx1 =R sx1 +jX sx1 ]]> <![CDATA[Z sr1 =R sr1 +jX sr1 ]]> <![CDATA[Z sc1 =R sc1 +jX sc1 ]]> <![CDATA[U d1 ]]> <![CDATA[Z sx1 =R sx1 +jX sx1 ]]> <![CDATA[Z sr2 =R sr2 +jX sr2 ]]> <![CDATA[Z sc2 =R sc2 +jX sc2 ]]> <![CDATA[U d2 ]]> <![CDATA[Z sx2 =R sx2 +jX sx2 ]]> <![CDATA[Z sr3 =R sr3 +jX sr3 ]]> <![CDATA[Z sc3 =R sc3 +jX sc3 ]]> <![CDATA[U d3 <!-- 3 -->]]> <![CDATA[Z sx2 =R sx2 +jX sx2 ]]> <![CDATA[Z sr4 =R sr4 +jX sr4 ]]> <![CDATA[Z sc4 =R sc4 +jX sc4 ]]> <![CDATA[U d4 ]]> …… …… …… …… <![CDATA[Z sxn =R sxn +jX sxn ]]> <![CDATA[Z sr(2n-1) =R sr(2n-1) +jX sr(2n-1) ]]> <![CDATA[Z sc(2n-1) =R sc(2n-1) +jX sc(2n-1) ]]> <![CDATA[U d(2n-1) ]]> <![CDATA[Z sxn =R sxn +jX sxn ]]> <![CDATA[Z sr(2n) =R sr(2n) +jX sr(2n) ]]> <![CDATA[Z sc(2n) =R sc(2n) +jX sc(2n) ]]> <![CDATA[U d(2n) ]]>

[0054] S2. Based on each set of no-load test data, calculate multiple system impedances corresponding to different test conditions and the resistance and inductance values corresponding to each system impedance. Specifically, perform the following operations:

[0055] The equation group is established based on each group of no-load test data obtained:

[0056]

[0057] Where n is a positive number, representing the total number of test conditions; U d is the voltage drop amplitude; R sr The resistor of the current limiting impedance, X sr is the inductor of the current limiting impedance; R sc is the resistance of the short-circuit impedance, X sc is the inductance of the short-circuit impedance; R sx is the resistance of the system impedance, X sxThe inductance is the system impedance;

[0058] According to the above equations, the resistance of the system impedance corresponding to all test conditions is {R sx1 ,R sx2 ,...,R sxn}, the inductance of the system impedance corresponding to all test conditions is {X sx1 ,X sx2 ,...,X sxn}.

[0059] S3. Calculate the average resistance and inductance values based on the resistance and inductance values corresponding to each system impedance, and ultimately determine the system impedance at the access point between the low-voltage fault generating device and the high-voltage side of the wind turbine step-up transformer. This controls the voltage drop amplitude and phase jump during the low-voltage ride-through capability test of the wind turbine fault. Specifically, perform the following operations:

[0060] According to the resistance value {R sx1 ,R sx2 ,...,R sxn} and the inductance {X sx1 ,X sx2 ,...,X sxn}, calculate the average resistance R and the average inductance X:

[0061]

[0062]

[0063] Where i is a positive number; n is a positive number representing the total number of test conditions;

[0064] Finally determine the system impedance Z of the connection point between the low voltage fault generating device and the high voltage side of the wind turbine step-up transformer:

[0065] Z=R+jX.

[0066] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, any changes made based on the shape and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for indirectly measuring system impedance based on a low voltage fault generating device, wherein the low voltage fault generating device is connected in series to the high voltage side of a step-up transformer of a wind turbine generator set, characterized in that: The low voltage fault generating device is electrically connected to the external power grid and includes a system impedance Z in series. sx , current limiting impedance Z sr and short-circuit impedance Z sc The current limiting impedance Zsr is used to limit the impact of the fault voltage on the power grid and other wind turbines in the wind farm. The calculation formula is: Z sr =R sr +jX sr , Among them, R sr The resistor of the current limiting impedance, X sr is the inductor of the current-limiting impedance; The short-circuit impedance Z sc The voltage drop required for the test is generated at the access point and is calculated as follows: Z sc =R sc +jX sc , Among them, R sc is the resistance of the short-circuit impedance, X sc The inductance is the short-circuit impedance; The system impedance Z sx The calculation formula is: Z sx =R sx +jX sx , Among them, R sx is the resistance of the system impedance, X sx The inductance is the system impedance; The method comprises the following steps: S1. For different test conditions, use the low voltage fault generating device to perform multiple no-load tests to obtain multiple sets of no-load test data corresponding to different test conditions. Specifically, perform the following operations: Under each test condition, two no-load tests with different voltage drop amplitudes were performed using a low-voltage fault generator. That is, under the premise of the same system impedance and two different voltage drop amplitudes, two different sets of current-limiting impedances and short-circuit impedances were calculated, which are the no-load test data under the corresponding test condition. S2. Calculate, based on each set of no-load test data, multiple system impedances corresponding to different test conditions and the resistance and inductance values corresponding to each system impedance; S3. Calculate the average resistance and inductance values based on the resistance and inductance values corresponding to each system impedance, and ultimately determine the system impedance of the access point between the low-voltage fault generating device and the high-voltage side of the wind turbine step-up transformer, thereby controlling the voltage drop amplitude and phase jump during the low-voltage ride-through capability test of the wind turbine fault.

2. The method for indirect measurement of system impedance based on a low voltage fault generating device according to claim 1, characterized in that: In step S2, the following operations are specifically performed: The equation group is established based on each group of no-load test data obtained: Where n is a positive number, representing the total number of test conditions; U d is the voltage drop amplitude; R sr The resistor of the current limiting impedance, X sr is the inductor of the current limiting impedance; R sc is the resistance of the short-circuit impedance, X sc is the inductance of the short-circuit impedance; R sx is the resistance of the system impedance, X sx The inductance is the system impedance; According to the above equations, the resistance of the system impedance corresponding to all test conditions is {R sx1 ,R sx2 ,...,R sxn }, the inductance of the system impedance corresponding to all test conditions is {X sx1 ,X sx2 ,...,X sxn }.

3. The method for indirect measurement of system impedance based on a low voltage fault generating device according to claim 1, characterized in that: In step S3, the following operations are specifically performed: According to the resistance value {R sx1 ,R sx2 ,...,R sxn } and the inductance {X sx1 ,X sx2 ,...,X sxn }, calculate the average resistance R and the average inductance X: Where i is a positive number; n is a positive number representing the total number of test conditions; Finally determine the system impedance Z of the connection point between the low voltage fault generating device and the high voltage side of the wind turbine step-up transformer: Z=R+jX 。

Images