Dq impedance measurement method for grid-connected converters

Abstract

The application discloses a kind of dq impedance measurement methods of grid-connected converter, comprising: S1. in the grid side injection disturbance frequency is ω p Three-phase symmetric disturbance voltage V p (ω p ), and response current I p (ω p ) and I p (2ω1-ω p ) are measured to obtain;Wherein, ω1 is grid angular frequency;S2. based on disturbance voltage and response current, self-admittance Y SA (ω p ) and accompanying admittance Y AA (ω p ) are calculated;S3. according to self-admittance Y SA (ω p ) and accompanying admittance Y AA (ω p ), dq impedance is calculated.The application can avoid the measurement error generated by synchronous phase angle disturbance, and high accuracy.

Description

Technical Field

[0001] This invention relates to the field of grid-connected converters, and more specifically to a method for measuring the dq impedance of a grid-connected converter. Background Technology

[0002] In recent years, with the development of renewable energy power generation technology, distributed power generation models of new energy sources, represented by wind power and photovoltaics, have been widely applied. Grid-connected converters, as the main interface of new energy grid-connected systems, are widely used in practical engineering. However, harmonic oscillation events can occur in new energy grid-connected systems during operation, leading to large-scale wind turbine disconnection. The main reason is that grid-connected converters have strong nonlinear characteristics, making them prone to system interactions and inducing harmonic oscillations.

[0003] To analyze system stability and avoid harmonic oscillations, many scholars have proposed stability analysis methods applicable to renewable energy grid-connected systems, building upon Middlebrook's impedance analysis method. These methods determine system stability by analyzing the ratio of the converter's impedance to the grid impedance. A positive stability margin in the impedance ratio indicates stable system operation; conversely, a negative margin indicates instability and harmonic oscillations.

[0004] Therefore, obtaining the converter impedance is particularly important and is key to judging system stability. Currently, converter impedance is mainly measured using a stationary coordinate system. However, this method is coupled with the grid impedance, meaning the measured converter impedance contains information about the grid impedance. This makes accurate analysis of the measured converter impedance difficult under different grid conditions; that is, as the grid impedance changes under different grid conditions, the converter impedance will also change.

[0005] Therefore, to solve the above problems, a method for measuring the dq impedance of grid-connected converters is needed. Summary of the Invention

[0006] In view of this, the purpose of this invention is to overcome the defects in the prior art and provide a method for measuring the dq impedance of grid-connected converters, which can avoid measurement errors caused by synchronous phase angle disturbances and has high accuracy.

[0007] The method for measuring the dq impedance of a grid-connected converter according to the present invention includes the following steps:

[0008] S1. Inject a disturbance with frequency ω into the power grid side. p Three-phase symmetrical disturbance voltage V p (ω p And the response current I was measured. p (ω p ) and I p (2ω1-ω p); where ω1 is the angular frequency of the power grid;

[0009] S2. Based on the disturbance voltage and response current, the self-admittance Y is calculated. SA (ω p ) and accompanying admittance Y AA (ω p );

[0010] S3. Based on self-guided admittance Y SA (ω p ) and accompanying admittance Y AA (ω p The dq impedance is calculated.

[0011] Furthermore, V is determined according to the following formula. p (ω p ):

[0012] V p (ω p ) = V ab +V bc e jπ / 3 ;

[0013] Among them, V ab V bc All are related to V p (ω p Line voltages with the same frequency; j represents the imaginary unit.

[0014] Furthermore, I is determined according to the following formula. p (ω p ):

[0015]

[0016] Among them, I a and I b All are related to I p (ω p Line currents with the same frequency; j represents the imaginary unit.

[0017] Furthermore, when 2ω1-ω p When >0,

[0018] When 2ω1-ω p When ≤0,

[0019] Among them, I a and I b All are related to I p (ω p Line currents with the same frequency; j represents the imaginary unit.

[0020] Furthermore, the self-admittance Y is determined according to the following formula. SA (ω p ):

[0021]

[0022] Furthermore, the accompanying admittance Y is determined according to the following formula. AA (ω p ):

[0023]

[0024] in, It represents the conjugate of the disturbance voltage.

[0025] Furthermore, the dq impedance is determined according to the following formula:

[0026]

[0027]

[0028]

[0029]

[0030] Among them, Y dd (s) is the admittance, which is the ratio of d-axis current to d-axis voltage; Y dq (s) is the admittance, which is the ratio of d-axis current to q-axis voltage; Y qd (s) is the admittance, which is the ratio of q-axis current to d-axis voltage; Y qq (s) is the admittance, which is the ratio of q-axis current to q-axis voltage; Y AA (s+jω1) * For accompanying admittance Y AA (s) is the conjugate of the frequency shifted to the left by ω1; Y SA (s+jω1) represents the self-admittance Y SA (s) The variable shifted to the left by ω1 frequency; Y AA (-s-jω1) represents the accompanying admittance Y. AA (-s) is the variable shifted to the right by ω1 frequency; Y SA (-s-jω1) * For self-guided nano-Y SA (-s) is the conjugate of the frequency shifted to the right by ω1; j represents the imaginary unit, s represents the complex frequency, and s is related to the perturbation frequency ω. p The relationship is s = jω p .

[0031] The beneficial effects of this invention are as follows: The dq impedance measurement method for grid-connected converters disclosed in this invention avoids the influence of synchronous phase angle disturbances on the dq impedance measurement structure by directly utilizing the measurement of self-admittance and accompanying admittance. Furthermore, the measurement method is a completely black-box measurement, requiring no knowledge of the converter's internal control structure and parameters, thus avoiding the problem of manufacturers not disclosing the converter's control structure and parameters. Attached Figure Description

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0033] Figure 1 This is a schematic diagram of the dq impedance measurement method of the present invention;

[0034] Figure 2 Y, the present invention dd Mathematical model and measurement effect diagram;

[0035] Figure 3 Y, the present invention dq Mathematical model and measurement results diagram;

[0036] Figure 4 Y, the present invention qq Mathematical model and measurement results diagram. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings, as shown in the figures:

[0038] The method for measuring the dq impedance of a grid-connected converter according to the present invention includes the following steps:

[0039] S1. Inject a disturbance with frequency ω into the power grid side. p Three-phase symmetrical disturbance voltage V p (ω p And the response current I was measured. p (ω p ) and I p (2ω1-ω p ); where ω1 is the angular frequency of the power grid;

[0040] S2. Based on the disturbance voltage and response current, the self-admittance Y is calculated. SA (ω p ) and accompanying admittance Y AA (ω p );

[0041] S3. Based on self-guided admittance Y SA (ω p ) and accompanying admittance Y AA (ω p The dq impedance is calculated.

[0042] In this embodiment, the converter is connected to an ideal power grid, and a frequency of ω is injected on the grid side. p The three-phase symmetrical disturbance voltage is denoted as V. p (ω p After injecting a disturbance voltage, the measured response current is expressed as I. p (ω p ) and I p (2ω1-ω p For example, frequency ω p The value is f p Then the disturbance voltage is V p (f p Of course, the frequency ω p Other frequency values ​​can also be selected, thus enabling measurements at all frequencies.

[0043] Through voltage V p (ω p ) and current I p (ω p ), I p (2ω1-ω p ), representing self-guided nanometer Y SA and accompanying admittance Y AA :

[0044]

[0045]

[0046] In the above formula (2), It represents the conjugate of the disturbance voltage.

[0047] Measured voltage V p (ω p It can be determined by the line voltage V. ab and V bc It means that, among them, V ab V bc All are related to V p (ω p Line voltages with the same frequency;

[0048] Current I p (ω p It can be determined by the line current I. a and I b It indicates that, among them, I a and I b All are related to I p (ω p Line currents with the same frequency;

[0049]

[0050] V p (ω p ) = V ab +V bc e jπ / 3 (4)

[0051] Among them, the time-domain voltage and current signal I is obtained using FRA. a I b V ab V bc The FRA mentioned is an existing frequency response analysis technique, which will not be described in detail here.

[0052] Furthermore, the measured current I p (2ω1-ω p ) can be made by I a and I b This means, for example, ω1 takes the value f0, ω p The value is f p ,but:

[0053] When 2f0-f p When >0, it is represented as:

[0054]

[0055] When 2f0-f p When ≤0, it is represented as:

[0056]

[0057] Using the measured Y SA (ω p ) and Y AA (ω p ) represents the dq impedance of the converter, i.e., Y dd (s), Y dq (s), Y qd (s) and Y qq (s). Y dd (s), Y dq (s), Y qd (s) and Y qq (s) represents the measured dq impedance, which is composed of these four elements. The relationships between them are as follows:

[0058]

[0059]

[0060]

[0061]

[0062] Among them, Y dd (s) is the admittance, which is the ratio of d-axis current to d-axis voltage; Y dq (s) is the admittance, which is the ratio of d-axis current to q-axis voltage; Y qd (s) is the admittance, which is the ratio of q-axis current to d-axis voltage; Y qq (s) is the admittance, which is the ratio of q-axis current to q-axis voltage; Y AA (s+jω1) * For accompanying admittance Y AA (s) is the conjugate of the frequency shifted to the left by ω1; Y SA (s+jω1) represents the self-admittance Y SA (s) The variable shifted to the left by ω1 frequency; Y AA (-s-jω1) represents the accompanying admittance Y. AA (-s) is the variable shifted to the right by ω1 frequency; Y SA (-s-jω1) * For self-guided nano-Y SA (-s) is the conjugate of the frequency shifted to the right by ω1; j represents the imaginary unit, s represents the complex frequency, and s is related to the perturbation frequency ω. p The relationship is s = jω p .

[0063] To better understand the dq impedance measurement method of this invention, a simulation comparison analysis is conducted between the measurement method of this invention and an analytical method using a mathematical model. The simulation results are as follows: Figure 2 , Figure 3 , Figure 4 As shown. Note that Y... qd (s) Since the voltage and current disturbances corresponding to the dq axis coordinate system are small, they are ignored.

[0064] Figure 2 , Figure 3 , Figure 4 In the diagram, the solid lines represent the analytical values ​​from the mathematical model, and the dots represent the measurement results obtained using the method of this invention. As can be seen, the measurement results agree well with the analytical values, demonstrating the effectiveness of the measurement method of this invention.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring the dq impedance of a grid-connected converter, characterized in that: Includes the following steps: S1. Injecting a disturbance frequency of [frequency missing] on the grid side. Three-phase symmetrical disturbance voltage And the response current was measured. and ;in, The angular frequency of the power grid; S2. The self-admittance is calculated based on the disturbance voltage and response current. and accompanying admittance ; S3. Based on self-admittance and accompanying admittance The dq impedance is calculated. The dq impedance is determined using the following formula: ； ； ； ； in, The admittance is the ratio of d-axis current to d-axis voltage. This is the admittance, which is the ratio of d-axis current to q-axis voltage. The admittance is the ratio of q-axis current to d-axis voltage; This is the admittance, which is the ratio of q-axis current to q-axis voltage. For accompanying admittance Conjugate quantity after frequency; For self-guided intake Variables following frequency; For accompanying admittance Variables following frequency; For self-guided intake Shift to the right Conjugate quantity after frequency; Represents the imaginary unit. Represents complex frequency, With disturbance frequency The relationship is .

2. The method for measuring the dq impedance of a grid-connected converter according to claim 1, characterized in that: Determined according to the following formula : ； in, , All are with Line voltages with the same frequency; It represents the imaginary unit.

3. The method for measuring the dq impedance of a grid-connected converter according to claim 1, characterized in that: Determined according to the following formula : ； in, and All are with Line currents with the same frequency; It represents the imaginary unit.

4. The method for measuring the dq impedance of a grid-connected converter according to claim 1, characterized in that: when hour, ; when hour, ; in, and All are with Line currents with the same frequency; It represents the imaginary unit.

5. The method for measuring the dq impedance of a grid-connected converter according to claim 1, characterized in that: The self-admittance is determined using the following formula. : 。 6. The method for measuring the dq impedance of a grid-connected converter according to claim 1, characterized in that: The accompanying admittance is determined using the following formula. : ； in, It represents the conjugate of the disturbance voltage.

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