A Method for Quantitative Analysis of Sideband Secondary Harmonic Emission Characteristics of Grid-Connected Converters

Abstract

The present invention discloses a technology in the field of harmonic analysis of grid-connected converters, and particularly relates to a method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter, including: defining the sampling sideband secondary harmonic frequency and the PWM sideband secondary harmonic frequency; selecting the f s -f p component, the f p +f0 component, and the f c -f p -f0 component, and modeling their harmonic emission characteristics; defining the background disturbance voltage of the distribution network and the frequency secondary harmonic currents of the three components; calculating the secondary harmonic voltage formed at the grid connection point; calculating the secondary harmonic voltage and current output by the sampler; calculating the modulation signal output by the controller; calculating the harmonic components of the grid-connected converter port voltage; calculating the secondary harmonic current in the grid-connected current of the grid-connected converter; constructing a quantitative analysis model. The quantitative analysis method fills the research gap in the existing quantitative analysis of sideband secondary harmonics of grid-connected converters and is of great significance for the analysis of harmonic and resonance problems in new power systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of harmonic analysis of grid-connected converters, and particularly relates to a method for quantitatively analyzing the emission characteristics of sideband secondary harmonics of grid-connected converters. Background Technique

[0002] As a key interface device for new energy grid connection, the number of grid-connected converters deployed in the power grid has increased significantly. However, there are sideband effects in the A / D sampling link and the PWM link in the control system of grid-connected converters during signal processing. When there is a background disturbance with a frequency of fp at the grid connection point, under the action of the sideband effect, the grid-connected converter will not only affect the magnitude of the disturbance frequency component, but also generate a series of sideband secondary harmonic components centered on the sampling and switching frequencies. The sampling and PWM sideband secondary harmonics generated by the sideband effect are an important source of grid harmonic pollution. Existing research on the sideband secondary harmonics of grid-connected converters mainly focuses on qualitative analysis, and quantitative analysis that can accurately reflect the emission characteristics of the sideband secondary harmonics of grid-connected converters is still blank. Therefore, considering the frequency coupling effect between the sampling and PWM sideband secondary harmonics and the disturbance frequency component, establishing a quantitative analysis model that can accurately reflect the emission characteristics of the sampling and PWM sideband secondary harmonics of grid-connected converters under the action of any frequency background disturbance has become a technical problem to be solved urgently. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for quantitatively analyzing the emission characteristics of sideband secondary harmonics of grid-connected converters, which is characterized by including the following steps:

[0004] Step 1: Define the frequency of the A / D sampling sideband secondary harmonics as ±n s f s ±n p f p , and the frequency of the PWM sideband secondary harmonics as ±n c f c ±n0 f0±n p f p , where f p is the frequency of the background disturbance voltage, f s is the sampling frequency of the grid-connected converter controller, f c is the switching frequency, f0 is the power grid power frequency signal frequency, n s , n c , n p , n0 = 0, 1, 2, 3...;

[0005] Step 2: Select the f s -f p component, the f c -f p -f0 component, and the f p +f0 component;

[0006] Step 3: Define the background disturbance voltage of the distribution network as The background disturbance frequency current in the grid-connected current of the grid-connected converter is f s -f p The frequency secondary harmonic current of the component is f c -f p The frequency secondary harmonic current of the -f0 component is f p The frequency secondary harmonic current of the +f0 component is

[0007] Step 4: Use the background disturbance frequency current in Step 3 and the frequency secondary harmonic current to calculate the f formed at the grid connection point s -f p frequency secondary harmonic voltage f c -f p -f0 frequency secondary harmonic voltage and the f p +f0 frequency secondary harmonic voltage

[0008] Step 5: Use the secondary harmonic voltage formed at the grid connection point in Step 4 to calculate the f sampled by the sampler p frequency harmonic voltage f s -f p frequency secondary harmonic voltage f c -f p -f0 frequency secondary harmonic voltage and the f p +f0 frequency secondary harmonic voltage

[0009] Step 6: Calculate the f sampled by the sampler p frequency harmonic current f s -f p frequency secondary harmonic current f c -f p -f0 frequency secondary harmonic current and the f p +f0 frequency secondary harmonic current

[0010] Step 7: Use the harmonic current in Step 6 and the secondary harmonic current Calculate the f output by the controller p Frequency modulation signal f s -f p Frequency modulation signal f c -f p -f0 frequency modulation signal And f p +f0 frequency modulation signal

[0011] Step 8: Modulate the signal according to the controller output in Step 7, and calculate the f p Frequency harmonic component f s -f p Frequency harmonic component f c -f p -f0 frequency harmonic component f p +f0 frequency harmonic component

[0012] Step 9: Use the harmonic components of the grid-connected converter port voltage in Step 8 Calculate the background disturbance frequency current in the grid-connected converter grid-connected current f s -f p Frequency secondary harmonic current of the component f c -f p Frequency secondary harmonic current of the -f0 component f p Frequency secondary harmonic current of the +f0 component

[0013] Step 10: Construct a quantization analysis model determined by the background disturbance voltage of the distribution network Determined by Quantification analysis model of

[0014] The secondary harmonic voltage formed by the grid connection point Is defined as:

[0015]

[0016] Where, Z g (jω p1 ), Z g (jω p2 ), Z g (jω p3 ) are all system impedances

[0017] The f output by the samplerp Frequency harmonic voltage f s -f p Frequency sub-harmonic voltage f c -f p Sub-harmonic voltage of -f0 and f p Sub-harmonic voltage of +f0 The specific definitions are as follows:

[0018]

[0019] Where: G af (jω) is the transfer function of the anti-aliasing filter, and * represents the conjugate form of the phasor.

[0020] The f p frequency harmonic current output by the sampler f s -f p Frequency sub-harmonic current f c -f p Sub-harmonic current of -f0 and f p Sub-harmonic current of +f0 The specific definitions are as follows:

[0021]

[0022] The f p frequency modulation signal output by the controller f s -f p Frequency modulation signal f c -f p Sub-harmonic modulation signal of -f0 and f p Sub-harmonic modulation signal of +f0 The definitions are as follows:

[0023]

[0024] Where: G d (jω) is the transfer function of the equivalent delay link, and G I (jω) is the transfer function of the inner-loop control.

[0025] The f p frequency harmonic component in the grid-connected converter port voltage f s -f p Frequency harmonic component fc -f p -f0 frequency harmonic component f p +f0 frequency harmonic component is defined as:

[0026]

[0027] wherein: is the co-frequency transfer coefficient of the modulation signal and the port voltage,

[0028] is the multi-frequency coupling coefficient of the modulation signal and the port voltage.

[0029] In the grid-connected current of the grid-connected converter, the component is defined as:

[0030]

[0031] wherein: G F1 (jω) and G F2 (jω) are the transfer functions of the LCL filtering link, and the specific forms are as follows:

[0032]

[0033] wherein, L1 is the filtering inductor on the port side of the LCL filter, L2 is the filtering inductor on the grid-connected side of the LCL filter, and C1 is the filtering capacitor in the LCL filter.

[0034] The quantitative analysis model is specifically:

[0035]

[0036] wherein: Y p , Y p1 , Y p2 , Y p3 are the transfer coefficients of the background disturbance voltage and the sideband secondary harmonic current.

[0037] In step 1, the PWM uses symmetric regular sampling, that is: f s = f c .

[0038] In step 1, the PWM can also use asymmetric regular sampling, that is: f s = 2f c

[0039] The beneficial effects of the present invention are as follows:

[0040] The present invention discloses a quantitative analysis method for the sideband secondary harmonic emission characteristics of a grid-connected converter. Considering the frequency coupling effect between the sampling and PWM sideband secondary harmonics and the background disturbance frequency components, a quantitative analysis model for the secondary harmonic emission characteristics of the grid-connected converter output current is established. The quantitative analysis model is more accurate and comprehensive compared with the prior art, specifically manifested in:

[0041] 1) Compared with the prior art which is only limited to the qualitative analysis of sideband secondary harmonics, a quantitative analysis method for the sideband secondary harmonic emission characteristics of a grid-connected converter disclosed by the present invention can accurately model and analyze the harmonic emission characteristics of the f s -f p component, the f p +f0 component, and the f c -f p -f0 component with relatively high contents in the sampling and PWM sideband secondary harmonics of the grid-connected converter.

[0042] 2) Compared with the modeling method in the prior art that ignores the influence of system impedance, the present invention considers the interaction between the sideband secondary harmonic current and the system impedance during the modeling process, and includes the sideband secondary harmonic voltage component during the sampling of the grid-connected point voltage, which can effectively improve the accuracy of the model.

[0043] 3) Compared with the modeling method in the prior art that only considers its own frequency components for the output voltage and current of the sampler, the present invention considers the frequency coupling effect caused by the sideband effect during the sampling process in the modeling of the output voltage and current of the sampler. Each frequency component of the output voltage and current of the sampler consists of its own frequency component and the sideband coupling component of other frequency components. The modeling process of the present invention is more accurate.

[0044] 4) Compared with the modeling method in the prior art that only considers its own frequency components during the PWM modulation process, the present invention considers the frequency coupling effect caused by the sideband effect during the PWM modulation process in the modeling of the grid-connected converter port voltage. Each frequency component of the grid-connected converter port voltage consists of its own frequency component and the sideband coupling component of other frequency components. Therefore, the modeling process of the present invention is more accurate and comprehensive.

[0045] In summary, the present invention discloses a quantitative analysis method for the sideband secondary harmonic emission characteristics of a grid-connected converter, which makes up for the research gap in the quantitative analysis of sideband secondary harmonics of existing grid-connected converters and is of great significance for the analysis of harmonic and resonance problems in new power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a flowchart of a quantitative analysis method for the sideband secondary harmonic emission characteristics of a grid-connected converter disclosed by the present invention;

[0047] Figure 2 It is a simplified block diagram of the structure and control of a grid-connected converter including sampling and PWM links;

[0048] Figure 3 It is a closed-loop control block diagram of a grid-connected converter considering the frequency coupling of sampling and PWM sideband secondary harmonics;

[0049] Figure 4 It is a control block diagram of the VSC inner loop control;

[0050] Figure 5 It is a waveform diagram of the output current;

[0051] Figure 6(a) is a comparison diagram of the theoretical analysis and test results of the fundamental and secondary harmonic current contents of the grid-connected converter;

[0052] Figure 6(b) is a comparison diagram of the theoretical analysis and test results of the fundamental and secondary harmonic phases of the grid-connected converter. Specific implementation manners

[0053] The present invention provides a method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter. The following further describes the present invention in detail with reference to the accompanying drawings.

[0054] As Figure 1 shown, an embodiment of the present invention discloses a method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter, including:

[0055] Step 1: Define the frequencies of the A / D sampling sideband secondary harmonics as ±n s f s ±n p f p and the frequencies of the PWM sideband secondary harmonics as ±n c f c ±n0 f0±n p f p where f p is the frequency of the background disturbance voltage, f s is the sampling frequency of the grid-connected converter controller, f c is the switching frequency, f0 is the power grid power frequency signal frequency, and n s 、n c 、n p 、n0 = 0, 1, 2, 3….

[0056] The structure and control simplified block diagram of the grid-connected converter is as Figure 2 shown. An LCL filter is used for filtering on the port side of the grid-connected converter. The complete control process includes: grid-connected current i g and grid connection point voltage u gFirst, the high-frequency components are filtered out by an anti-aliasing filter; then, it enters the control link after A / D sampling processing; after being processed by control links such as the voltage outer loop and current inner loop, a modulation signal M is generated. abc , the modulation signal is converted into a continuous signal through the ZOH link, and then a switching signal S is generated through PWM modulation. abc ; Under the control of the switching signal, the grid-connected converter realizes closed-loop operation. The sampling frequency of the grid-connected converter controller is denoted as f. s , the switching frequency is denoted as f. c , and the power grid power frequency signal frequency is f0. When there is a background disturbance voltage with a frequency of f p in the distribution network, under the action of sampling and PWM sideband effects, a series of sampling sideband secondary harmonics with frequencies of ±n s f s ±n p f p (n s , n p = 0, 1, 2, 3...), and a series of PWM sideband secondary harmonics with frequencies of ±n c f c ±n0 f0 ± n p f p (n c , n p , n0 = 0, 1, 2, 3...).

[0057] The sampling frequency of the grid-connected converter is generally synchronized with the switching frequency. When PWM is symmetric regular sampling, f s = f c , when PWM is asymmetric regular sampling, f s = 2f c . The quantization analysis model disclosed in this embodiment can be applicable to one of the above two sampling methods. Since the PWM sideband secondary harmonic components are richer during symmetric regular sampling compared to asymmetric regular sampling, and the frequency coupling relationship between them and the disturbance frequency components will be more complex, symmetric regular sampling is selected in this embodiment, that is, f s = f c for processing.

[0058] Step 2: Considering that the port filter of the grid-connected converter, the anti-aliasing filter at the front end of the A / D sampling link, and the low-pass characteristics of the controller have a significant inhibitory effect on the sampling and PWM sideband secondary harmonic components above the sampling frequency, the present invention selects the components of f sc - f p , f c - f p - f0, and f p + f0, which have relatively higher contents below the sampling frequency, and models and analyzes the harmonic emission characteristics of the three components.

[0059] Step 3: Define the background disturbance voltage of the distribution network as Define the background disturbance frequency current in the grid-connected current of the grid-connected converter as f s -f p Define the frequency secondary harmonic current as f c -f p Define the -f0 frequency secondary harmonic current as f p Define the +f0 frequency secondary harmonic current as

[0060] Compared with the prior art which is only limited to the qualitative analysis of sideband secondary harmonics, a method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter disclosed in the present invention can accurately model and analyze the harmonic emission characteristics of the components with higher contents in the sampled and PWM sideband secondary harmonics of the grid-connected converter, namely, the f s -f p component, the f p +f0 component, and the f c -f p -f0 component.

[0061] Step 4: When the system impedance cannot be ignored, the sideband secondary harmonic current acts with the system impedance Z g Use the background disturbance frequency current in Step 3 and the frequency secondary harmonic current to calculate the specific definitions of the f s -f p frequency secondary harmonic voltage f c -f p -f0 frequency secondary harmonic voltage and the f p +f0 frequency secondary harmonic voltage formed at the grid connection point as:

[0062]

[0063] wherein, Z g (jω p1 ), Z g (jω p2 ), and Z g (jω p3 ) are all system impedances.

[0064] Compared with the modeling method in the prior art where the output voltage and current of the sampler only consider their own frequency components, in the modeling process of the output voltage and current of the sampler in the present invention, the frequency coupling effect caused by the sideband effect due to sampling is considered. Each frequency component of the output voltage and current of the sampler consists of its own frequency component and the sideband coupling component of other frequency components. The modeling process of the present invention is more accurate.

[0065] Step 5: Considering the frequency coupling effect caused by sampling and the filtering effect of the anti-aliasing filter, use the secondary harmonic voltage formed at the grid connection point in Step 4 to calculate the f p frequency harmonic voltage f s −f p frequency secondary harmonic voltage f c −f p −f0 frequency secondary harmonic voltage and the f p +f0 frequency secondary harmonic voltage The specific definitions are as follows:

[0066]

[0067] In the formula: * represents the conjugate form of the phasor, G af (jω) is the transfer function of the anti-aliasing filter. In this embodiment, a fourth-order Butterworth filter is selected as the anti-aliasing filter, which has relatively better filtering characteristics compared with the traditional second-order filter.

[0068] Step 6: Considering the frequency coupling effect caused by sampling and the filtering effect of the anti-aliasing filter, calculate the f p frequency harmonic current f s −f p frequency secondary harmonic current f c −f p −f0 frequency secondary harmonic current and the f p +f0 frequency secondary harmonic current The specific definitions are as follows:

[0069]

[0070] Compared with the modeling method in the prior art where the output voltage and current of the sampler only consider their own frequency components, in the modeling process of the output voltage and current of the sampler in the present invention, the frequency coupling effect caused by the sideband effect caused by sampling is considered. Each frequency component of the output voltage and current of the sampler consists of its own frequency component and the sideband coupling component of other frequency components. The modeling process of the present invention is more accurate.

[0071] Step 7: Use the harmonic current in Step 6 and the secondary harmonic current Considering links such as the current inner loop, grid-side voltage feedforward, and controller equivalent delay, calculate the f output by the controller p frequency modulation signal f s -f p frequency modulation signal f c -f p -f0 frequency modulation signal and f p +f0 frequency modulation signal The definitions are as follows:

[0072]

[0073] In the formula: G d (jω) is the transfer function of the equivalent delay link. When the equivalent delay time constant is T s , the specific form is shown in Equation (41); G I (jω) is the inner loop control transfer function. Select PI control as the inner loop control method. The VSC inner loop control structure is as Figure 4 shown, and the specific expression is shown in Equation (42).

[0074] G d (jω) = e -jωT s (41)

[0075]

[0076] In the formula: ω0 is the angular frequency of the power grid power frequency signal.

[0077] As Figure 3 shown, in this implementation, the closed-loop control structure of the grid-connected converter considering the sampling and PWM sideband secondary harmonic frequency coupling is disclosed. Compared with the prior art, the control structure disclosed in this implementation includes the sampling coupling and PWM modulation coupling effects between different frequency components, and can more accurately reflect the emission characteristics of sampling and PWM sideband secondary harmonics.

[0078] Step 8: Considering the frequency coupling effect caused by PWM modulation, calculate the f p frequency harmonic component f s −f p frequency harmonic component f c −f p −f0 frequency harmonic component f p +f0 frequency harmonic component The specific definitions are as follows:

[0079]

[0080] In the formula: is the same-frequency transfer coefficient between the modulation signal and the port voltage, is the multi-frequency coupling coefficient between the modulation signal and the port voltage. The specific form is shown in Equation (51)

[0081]

[0082] In the formula: J i is the Bessel function of the first kind, i = (−1, 0, 1), M0 and θ0 are the amplitude and phase angle of the fundamental component in the modulation signal output by the controller, θ c is the initial phase of the carrier wave, M p 、M p1 、M p2 、M p3 are the amplitudes of the respective harmonic components in the modulation signal, θ p 、θ p1 、θ p2 、θ p3 are the initial phase angles of the respective harmonic components in the modulation signal, ω c is the angular frequency corresponding to f c ,ω p1 is the angular frequency corresponding to f s −f p ,ω p2 is the angular frequency corresponding to f c −f p −f0, ω p3 is the angular frequency corresponding to f p +f0.

[0083] Compared with the modeling method in existing research that only considers its own frequency components in the PWM modulation process, the present invention considers the frequency coupling effect caused by the sideband effect induced by PWM modulation in the modeling process of the grid-connected converter port voltage. Each frequency component of the grid-connected converter port voltage consists of its own frequency component and the sideband coupling components of other frequency components. Therefore, the modeling process of the present invention is more accurate and comprehensive.

[0084] Step 9: Use the harmonic components of the grid-connected converter port voltage in Step 8 to calculate the components in the grid-connected current of the grid-connected converter, specifically:

[0085]

[0086] In the formula: G F1 (jω) and G F2 (jω) are the transfer functions of the LCL filter link, and the specific form is shown in Equation (7).

[0087]

[0088] In the formula, L1 is the filter inductor on the port side of the LCL filter, L2 is the filter inductor on the grid-connected side of the LCL filter, and C1 is the filter capacitor in the LCL filter.

[0089] Step 10: Combine Steps 4 to 9, through substitution, simplification and arrangement, to construct a quantitative analysis model determined by the background disturbance voltage of , specifically:

[0090]

[0091] Y p , Y p1 , Y p2 , Y p3 are the transfer coefficients between the background disturbance voltage and each harmonic current, and the specific calculation process is as follows:

[0092] Based on Equations (1) to (7), the ratio relationship between the background disturbance frequency component in the grid-connected converter port voltage and the background disturbance voltage at the grid connection point can be calculated as:

[0093]

[0094] In Equation (9), H a1 , H a2 , H b1 , H b2 The specific expressions are shown in Equation (10).

[0095]

[0096] The parameters K in Equations (8) and (9) ai 、K bi 、K ci 、K di (i = 1, 2, 3, 4) The specific expressions are as shown in Equation (11).

[0097]

[0098] a in Equation (11) i (i = p, p1, p2, p3), b i (i = p, p1, p2, p3), c p 、d p1 The specific expressions are as shown in Equation (12).

[0099]

[0100] Using Equations (9) - (12), the ratio relationships between the three sideband secondary harmonic components in the grid - connected converter port voltage and the background disturbance voltage at the grid - connection point can be further calculated as follows:

[0101]

[0102] Thus, Y in Equation (8) p 、Y p1 、Y p2 、Y p3 The specific expressions are as follows

[0103]

[0104] To verify the effectiveness of a method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid - connected converter disclosed in this embodiment, a grid - connected converter experimental platform is built using the parameters shown in Table 1. The experimental platform consists of a DSP controller (TMS320F28069) and an RT - BOX hardware simulator. The quantitative analysis model disclosed in the present invention is used to predict the sideband secondary harmonic emission characteristics of the grid - connected converter.

[0105] Table 1 Main parameters of the grid - connected converter circuit and controller

[0106]

[0107] Under the rated power operation condition of the grid - connected converter, a three - phase symmetrical disturbance voltage with a frequency of 1125 Hz and a magnitude of 0.02U g is applied at the grid - connection point. The output current waveform of the grid - connected converter recorded by the oscilloscope is as Figure 5As shown. Select the phase A current for FFT analysis. The comparison between the amplitudes and phase angles of the disturbance frequency components and the sideband secondary harmonics and the theoretical analysis values is shown in Figures 6(a) and 6(b). It can be seen from the comparison that the error between the theoretical calculation results and the experimental test results of the primary and secondary harmonic current contents and phases of the grid-connected converter is extremely small. Therefore, the effectiveness of a method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter disclosed in this embodiment can be verified.

Claims

1. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter, characterized in that, Including the following steps: Step 1: Define the frequencies of the A / D sampling sideband secondary harmonics as ±n s , f s , ±n p , f p , and the frequencies of the PWM sideband secondary harmonics as ±n c , f c , ±n0, f0, ±n p , f p , where f p is the frequency of the background disturbance voltage, f s is the sampling frequency of the grid-connected converter controller, f c is the switching frequency, f0 is the grid power frequency signal frequency, and n s , n c , n p , n0 = 0, 1, 2, 3…; Step 2: Select f s -f p component, f c -f p -f0 component and f p +f0 component; Step 3: Define the background disturbance voltage of the distribution network as The background disturbance frequency current in the grid-connected current of the grid-connected converter is f s -f p The frequency secondary harmonic current of the component is f c -f p The frequency secondary harmonic current of the -f0 component is f p The frequency secondary harmonic current of the +f0 component is Step 4: Use the background disturbance frequency current in Step 3 and the frequency secondary harmonic current to calculate the f s -f p frequency secondary harmonic voltage f c -f p -f0 frequency secondary harmonic voltage and the f p +f0 frequency secondary harmonic voltage Step 5: Use the secondary harmonic voltage formed at the grid connection point in Step 4 Calculate the f output by the sampler p Frequency harmonic voltage f s −f p Frequency secondary harmonic voltage f c −f p −f0 frequency secondary harmonic voltage And f p +f0 frequency secondary harmonic voltage Step 6: Calculate f output by the sampler p Frequency harmonic current f s -f p Frequency sub-harmonic current f c -f p -f0 frequency sub-harmonic current and f p +f0 frequency sub-harmonic current Step 7: Use the harmonic current in Step 6 and the secondary harmonic current to calculate the f p frequency modulation signal f s −f p frequency modulation signal f c −f p −f0 frequency modulation signal and the f p +f0 frequency modulation signal Step 8: Calculate the f p frequency harmonic component f s -f p frequency harmonic component f c -f p -f0 frequency harmonic component f p +f0 frequency harmonic component Step 9: Utilize the harmonic components of the grid-connected converter port voltage in Step 8 Calculate the background disturbance frequency current in the grid-connected current of the grid-connected converter f s -f p Frequency secondary harmonic current of the component f c -f p Frequency secondary harmonic current of the -f0 component f p Frequency secondary harmonic current of the +f0 component Step 10: Construct a quantitative analysis model determined by the background disturbance voltage of the distribution network determined by ; The quantitative analysis model is specifically as follows: where: Y p , Y p1 , Y p2 , Y p3 are the transfer coefficients of the background disturbance voltage and the sideband secondary harmonic current.

2. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter according to claim 1, characterized in that, The secondary harmonic voltage formed by the connection point is defined as: Among them, Z g (jω p1 ), Z g (jω p2 ), Z g (jω p3 ) are all system impedances.

3. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter according to claim 1, characterized in that The f output by the sampler p Frequency harmonic voltage f s -f p Frequency sub-harmonic voltage f c -f p -f0 frequency sub-harmonic voltage And f p +f0 frequency sub-harmonic voltage The specific definitions are as follows: Where: G af (jω) is the transfer function of the anti-aliasing filter, and * represents the conjugate form of the phasor.

4. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter according to claim 3, characterized in that, The f output by the sampler p Frequency harmonic current f s -f p Frequency sub-harmonic current f c -f p Sub-harmonic current of -f0 frequency And f p Sub-harmonic current of +f0 frequency The specific definitions are as follows:

5. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter according to claim 1, characterized in that The f output by the controller p Frequency modulation signal f s -f p Frequency modulation signal f c -f p -f0 frequency modulation signal and f p +f0 frequency modulation signal are defined as: Where: G d (jω) is the transfer function of the equivalent delay link, G I (jω) is the transfer function of the inner loop control.

6. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter according to claim 1, characterized in that The f p frequency harmonic component f s -f p frequency harmonic component f c -f p -f0 frequency harmonic component f p +f0 frequency harmonic component is defined as: In the formula: is the same-frequency transfer coefficient of the modulation signal and the port voltage, is the multi-frequency coupling coefficient of the modulation signal and the port voltage.

7. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter according to claim 1, characterized in that The grid-connected current of the grid-connected converter is defined as: where: Z g (jω p1 ), Z g (jω p2 ), Z g (jω p3 ) are all system impedances, G F1 (jω) and G F2 (jω) are the transfer functions of the LCL filter link, and the specific forms are as follows: Wherein, L1 is the filter inductor on the port side of the LCL filter, L2 is the filter inductor on the grid connection side of the LCL filter, and C1 is the filter capacitor in the LCL filter.

8. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter according to claim 1, characterized in that In step 1, PWM uses symmetric rule sampling, i.e.: f s = f c .

9. A method for quantitatively analyzing the sideband secondary harmonic emission characteristics of a grid-connected converter according to claim 1, characterized in that In step 1, PWM can also use asymmetric regular sampling, i.e.: f s = 2f c .

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