A high proportion of renewable energy conversion device impedance regulation capability analysis method

Abstract

The application provides a high-proportion renewable energy variable flow device impedance regulation capability analysis method, and belongs to the field of energy, and comprises the following steps: constructing a PCC point voltage expression and a variable flow device current frequency domain expression without considering a PWM (pulse width modulation) nonlinear link; the PCC point represents a common connection point; based on the PCC point voltage expression without considering the PWM nonlinear link, a PCC point voltage expression in a frequency domain considering the PWM nonlinear link is constructed; based on the variable flow device current frequency domain expression without considering the PWM nonlinear link and the PCC point voltage expression in the frequency domain considering the PWM nonlinear link, a grid-connected inverter sequence impedance model considering the PWM nonlinear link is constructed, and is used for analyzing the impedance regulation capability of the renewable energy variable flow device. The application can capture the dynamic behavior of renewable energy power generation equipment, and provides an analysis tool for power grid operation and control.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of energy, and particularly relates to a high-proportion renewable energy variable flow device impedance regulation capability analysis method. BACKGROUND

[0002] The energy shortage problem is increasingly prominent in the world, and the demand for renewable energy in human society is increasing. Photovoltaic power generation system, as an important part of the current renewable power generation system, is widely used in the entire power system due to its environmental protection and non-pollution characteristics.

[0003] Photovoltaic power generation equipment is usually connected to the power grid through power electronic equipment, so its dynamic characteristics and control strategy have an important influence on the stability and power quality of the power grid. Especially under weak grid conditions, the impedance characteristics of photovoltaic power generation equipment have a significant impact on system stability. Therefore, accurate modeling of the impedance characteristics of photovoltaic power generation equipment is crucial for analyzing and designing its grid-connected control strategy.

[0004] Traditional impedance modeling methods include dq (direct axis and quadrature axis) impedance modeling in the synchronous rotating coordinate system and sequence impedance modeling in the stationary natural coordinate system. Although these two methods can describe the dynamic characteristics of renewable energy power generation equipment to some extent, they still have limitations. For example, these methods often ignore the nonlinear and time-varying characteristics of the inverter dynamic response, resulting in limited accuracy and applicability of the model. In addition, as the capacity of renewable energy power generation equipment increases and the grid conditions change, traditional modeling methods may not be able to adapt to new operating environments, thereby affecting the accuracy of system stability analysis.

[0005] Therefore, there is an urgent need for an improved high-proportion renewable energy variable flow device impedance regulation capability analysis method to better capture its dynamic characteristics. SUMMARY

[0006] To solve the above technical problems, the application provides a high-proportion renewable energy variable flow device impedance regulation capability analysis method, which improves the traditional converter sequence impedance modeling method by considering the nonlinear characteristics of the PWM (pulse width modulation) link based on the study of the topology and control method of photovoltaic power generation equipment, thereby improving the accuracy and applicability of the model. The improved model not only can more accurately capture the dynamic behavior of renewable energy power generation equipment, but also can adapt to different grid conditions, providing a more reliable analysis tool for grid operation and control.

[0007] To achieve the above purpose, the application adopts the following technical solution:

[0008] A high-proportion renewable energy variable flow device impedance regulation capability analysis method, comprising the following steps:

[0009] Step 1, constructing the PCC point voltage expression without considering the PWM nonlinear link and the current frequency domain expression of the converter; the PCC point represents the point of common coupling; PWM represents pulse width modulation;

[0010] Step 2, based on the PCC point voltage expression without considering the PWM nonlinear link, constructing the PCC point voltage expression considering the PWM nonlinear link in the frequency domain;

[0011] Step 3, based on the current frequency domain expression of the converter without considering the PWM nonlinear link and the PCC point voltage expression considering the PWM nonlinear link in the frequency domain, constructing the grid-connected inverter sequence impedance model considering the PWM nonlinear link, which is used for analyzing the impedance regulation capability of the renewable energy conversion device, capturing the dynamic behavior of the renewable energy generation equipment, and providing an analysis tool for grid operation and control.

[0012] Advantages:

[0013] The high-proportion renewable energy conversion device impedance regulation capability analysis method provided by the application applies the grid-connected inverter sequence impedance model considering the PWM nonlinear link to analyze the impedance regulation capability of the renewable energy conversion device, which can more accurately capture the dynamic behavior of the renewable energy generation equipment and provide a more reliable analysis tool for grid operation and control. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 A typical topology diagram for a photovoltaic power generation equipment (PV) connected to a grid through a converter;

[0015] Figure 2 A typical control block diagram of a photovoltaic inverter;

[0016] Figure 3a , Figure 3b A comparison diagram of the sequence impedance simulation value obtained by simulation and the theoretical value obtained by the analysis method provided by the application; wherein, Figure 3a is a positive sequence impedance comparison diagram, Figure 3b is a negative sequence impedance comparison diagram; Figure 3a (a) of, Figure 3b (a) of is an amplitude comparison diagram, Figure 3a (b) of, Figure 3b (b) of is a phase angle comparison diagram;

[0017] Figure 4 is a flowchart of a high-proportion renewable energy conversion device impedance regulation capability analysis method of the application. DETAILED DESCRIPTION

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0019] like Figure 4 As shown, the impedance regulation capability analysis method for a high-proportion renewable energy converter of the present invention includes the following steps:

[0020] Step 1: Construct the voltage expression for the point of common connection (PCC) and the frequency domain expression for the converter current without considering the nonlinearity of PWM (Pulse Width Modulation);

[0021] Step 2: Based on the PCC point voltage expression that does not consider the PWM nonlinearity, construct the PCC point voltage expression in the frequency domain that considers the PWM nonlinearity.

[0022] Step 3: Based on the frequency domain expression of the converter current without considering the PWM nonlinearity and the frequency domain expression of the PCC point voltage considering the PWM nonlinearity, construct a grid-connected inverter sequence impedance model considering the PWM nonlinearity. This model is used to analyze the impedance regulation capability of renewable energy converter devices, more accurately capture the dynamic behavior of renewable energy power generation equipment, and provide a more reliable analysis tool for grid operation and control.

[0023] Specifically, step 1 includes:

[0024] like Figure 1 The image shows a photovoltaic power generation device ( Figure 1 A typical topology in which PV (PV power) is connected to the grid via a converter, where C dc L is the DC-side capacitor of the converter. f C f These are the filter inductor and filter capacitor, respectively, L g and R g These represent the line inductance and resistance in the power grid, used to simulate line parameters in a real power system. The photovoltaic power generation equipment connects to the DC-side capacitor C of the converter. dc It is connected to the inverter, which inverts the DC power into AC power, and then connects to the PCC point through the LC filter. Figure 1 in, u a u b u c V is the midpoint voltage of the bridge arm of the grid-connected inverter. a v b v c The voltage at the PCC point where the grid-connected inverter is connected, u ga ugb , u gc is the grid voltage, i ga , i gb , i gc is the grid-connected current of the converter, V dc and I dc are the DC side voltage and current, respectively.

[0025] The significant nonlinear characteristics of the converter port determine that the core task of its impedance modeling is to linearize the nonlinear components inside the inverter, which is also the main task in the process of impedance model construction. By injecting positive and negative sequence disturbance voltages with an amplitude of no more than 10% of the rated voltage amplitude of the power frequency, the dynamic characteristics of the converter can be captured without affecting the stable operating point of the system.

[0026] Since the control of the grid-connected inverter is carried out in the synchronous rotating coordinate system, the equation in the synchronous coordinate system is given. Without considering the disturbance, the frequency domain expression of the PCC point voltage in the synchronous rotating coordinate system is:

[0027] (1)

[0028] where V1、 and φ1are the fundamental voltage amplitude, fundamental angular frequency and fundamental current initial phase angle, respectively; φ vp is the positive sequence disturbance voltage initial phase angle; φ vn is the negative sequence disturbance voltage initial phase angle, V d1 , V q1 are the frequency domain expressions of the PCC point voltage in the synchronous rotating coordinate system without considering the disturbance, V d1 [ω1] and V q1 [ω1] are the positive sequence direct-axis voltage and positive sequence quadrature-axis voltage at the PCC point in the synchronous rotating coordinate system, V d1 [-ω1] and V q1 [-ω1] are the negative sequence direct-axis voltage and negative sequence quadrature-axis voltage at the PCC point in the synchronous rotating coordinate system, V d1 [0] and V q1 [0] are the zero sequence direct-axis voltage and zero sequence quadrature-axis voltage at the PCC point in the synchronous rotating coordinate system, G v is the transfer function containing the sampling link and low-pass filter, s is the Laplace operator, and j is the imaginary unit. V p , V n are the positive sequence disturbance voltage amplitude and negative sequence disturbance voltage amplitude, respectively.

[0029] After considering the transfer function H PLL (s) of the phase-locked loop, the expression of the PCC point voltage in the synchronous rotating coordinate system in the frequency domain is:

[0030] (2)

[0031] where H PLL (s) is the transfer function of the phase-locked loop, G v (s) is the transfer function of the current sampling function and the low-pass filter.

[0032] To simplify the calculation process, the simplified phase-locked loop function is defined as T PLL (s), and , the current sampling function is G i , and the analog sampling low-pass filter and delay, then the frequency domain expression of the current is:

[0033] (3)

[0034] where I1, I p , and I n are the fundamental current amplitude, the positive sequence disturbance current amplitude, and the negative sequence disturbance current amplitude, respectively, θ i is the angle between the current phasor and the d-axis during coordinate transformation, and the subscript i indicates the current. Since it is the angle between the current phasor and the d-axis, the subscript is added, , which represents the base value of the angle. G i (s) is the current sampling function, and T PLL (s) is the phase-locked function defined in the foregoing. and represent the positive sequence direct-axis current and the positive sequence quadrature-axis current at the PCC point in the synchronous rotating coordinate system, respectively; and represent the negative sequence direct-axis current and the negative sequence quadrature-axis current at the PCC point in the synchronous rotating coordinate system, respectively; and represent the zero sequence direct-axis current and the zero sequence quadrature-axis current at the PCC point in the synchronous rotating coordinate system, respectively.

[0035] Specifically, the step 2 comprises:

[0036] When considering the nonlinear characteristics of the pulse width modulation (PWM) link of the grid-connected inverter, the dynamic process essentially constitutes a nonlinear system with time-varying properties. As the core parameter of the switching device control logic, the PWM modulation index can be defined as a nonlinear function m(t) of time variable, and its dynamic characteristics are affected by multiple nonlinear factors such as the time-varying characteristics of the carrier signal, the dynamic fluctuations of the modulation wave components, and the switching dead zone effect. This nonlinear function relationship is manifested as the non-steady coupling of the modulation parameters and the time variable in the time domain analysis, and its dynamic response presents a significant asymmetric harmonic distribution characteristic. The nonlinear function m(t) in the time domain can be represented as:

[0037] (4)

[0038] wherein v 载波 (t) is a carrier signal function, v 调制波 (t) is a modulating wave signal function, t is a time variable, ΔT is a non-linear distortion factor reflecting the dead-time of the switch, which is a dead-time adaptive correction term based on the polarity of the current, and satisfies:

[0039] (5)

[0040] wherein T dead is a preset dead-time, sgn is a sign function, i m represents the mth phase current. K comp is a linear constant, reflecting the non-linear characteristics of the current, and ε is a zero-preventing denominator constant.

[0041] After the time-domain nonlinearity is processed in the frequency domain by using the harmonic linearization theory, when the non-linear effect of the PWM link is considered, the expression of the PCC point voltage in the synchronous rotating coordinate system in the frequency domain is: (6)

[0042] wherein M is the frequency-domain expression of the linearized PWM modulation index. and represent the direct-axis voltage and the quadrature-axis voltage of the PCC point in the synchronous rotating coordinate system in the frequency domain, respectively. represents the frequency.

[0043] Specifically, the step 3 comprises:

[0044] As Figure 2 shown is a control block diagram of a photovoltaic grid-connected inverter, wherein i dr , i qr are the reference currents of the d-axis and the q-axis, respectively, θ PLL is the angle output by the phase-locked loop, H i is a current PI controller, K d is a current feedforward coefficient, and K f is a voltage feedforward coefficient. The voltage and the current in the three-phase (abc) stationary coordinate system are converted into the direct-axis and quadrature-axis currents in the dq coordinate system after coordinate transformation. The currents in the dq coordinate system are compared with the given values, and the comparison results are input into the current PI controller. The output of the current PI controller and the voltage feedforward quantity and the current feedforward quantity are calculated, and then the calculation results are subjected to coordinate transformation again, and the output is the voltage and the current in the three-phase stationary coordinate system. After PWM modulation, the output is used as the switching signal to control the inverter.

[0045] Then, the d-axis modulation wave C d and the q-axis modulation wave C q of the grid-connected inverter in the synchronous rotating coordinate system in the frequency domain are:

[0046] (7)

[0047] Among them, C d [ω1] and C q [ω1] represents the positive-sequence direct-axis modulation wave and the positive-sequence quadrature-axis modulation wave of the grid-connected inverter in the synchronous rotating coordinate system, respectively. d [-ω1] and C q [-ω1] represents the negative-sequence direct-axis modulation wave and the negative-sequence quadrature-axis modulation wave of the grid-connected inverter in the synchronous rotating coordinate system, respectively. d [0] and C q [0] represents the zero-sequence direct-axis modulation wave and the zero-sequence quadrature-axis modulation wave of the grid-connected inverter in the synchronous rotating coordinate system, respectively.

[0048] Combining equations (3), (5), (6), and (8), the sequence impedance model of the grid-connected inverter considering the PWM nonlinearity is obtained as follows:

[0049] (8)

[0050] Among them, L f For inverter filter inductance, V dc V is the DC-side voltage of the inverter, V1 is the amplitude of the inverter's fundamental voltage, ω1 is the fundamental angular frequency of the inverter, and K... d K f H represents the current and voltage feedforward coefficients, respectively. PI (s) is a current PI controller, G i (s) is the current sampling function. Indicates positive sequence impedance. This represents the negative sequence impedance.

[0051] To ensure the usability of the sequence impedance model, an adaptive parameter update mechanism is introduced, based on the positive sequence impedance change ΔZ. pdyn and negative sequence impedance change ΔZ ndyn The parameters of the sequence impedance model are dynamically adjusted. ΔZ pdyn and ΔZ ndyn The parameters of the sequence impedance model are dynamically adjusted. The adjustment formula is:

[0052] (9)

[0053] Among them, Z p (k+1) and Z n (k+1) represent the positive-sequence impedance and negative-sequence impedance of the (k+1)th iteration, respectively, Z p (k) and Z n (k) represent the positive-sequence impedance and negative-sequence impedance of the k-th iteration, respectively, and the convergence condition is that the Z-values ​​of adjacent iterations converge. p and Zn The amount of change in the amplitude-frequency characteristic at 50 Hz is less than 10 -3 . dω is the differential amount of frequency, ΔZ pdyn is the amount of change in positive sequence impedance, ΔZ ndyn is the amount of change in negative sequence impedance, K p and K i are proportional coefficient and integral coefficient respectively.

[0054] Embodiment:

[0055] A grid-connected inverter simulation model as shown in Figure 1 is established in simulation software, and specific parameters are shown in Table 1.

[0056] Table 1

[0057]

[0058] The purpose of monitoring the sequence impedance of the converter is achieved by injecting positive sequence or negative sequence voltage disturbance into the main circuit of the three-phase grid-connected inverter system controlled in the synchronous rotating coordinate system. The positive sequence disturbance voltage injection circuit adopts a positive sequence phase, and can simultaneously inject five positive sequence voltage signals of different frequencies into the main circuit, thereby achieving the inspection of the positive sequence impedance of the converter at five different frequency points. Similarly, the negative sequence disturbance voltage injection circuit adopts a negative sequence phase, and can simultaneously inject five negative sequence voltage signals of different frequencies into the main circuit, thereby achieving the inspection of the negative sequence impedance of the converter at five different frequency points. By changing the frequency of the disturbance voltage and performing cyclic simulation, the positive sequence or negative sequence impedance of the converter in multiple frequency bands can be detected.

[0059] The comparison chart of the sequence impedance simulation values obtained by simulation and the theoretical values obtained by the analysis method proposed in the present application is shown in Figure 3a , Figure 3b , wherein Figure 3a is a comparison chart of positive sequence impedance, Figure 3b is a comparison chart of negative sequence impedance. Among them, Figure 3a (a) of (a) is an amplitude comparison chart, Figure 3b (b) of (a) is a phase angle comparison chart, Figure 3a (b) of (b) is an amplitude comparison chart, Figure 3b (b) of (b) is a phase angle comparison chart.

[0060] It can be seen through comparison that the theoretical calculation result and the circuit simulation result have high consistency, and the analysis method proposed in the present application can accurately capture the dynamic behavior of renewable energy power generation equipment, and provide a more reliable analysis tool for power grid operation and control.

Claims

1. A method for analyzing the impedance regulation capability of a high-proportion renewable energy converter, characterized in that, Comprising the following steps: Step 1, constructing the PCC point voltage expression without considering the PWM nonlinear link and the converter current frequency domain expression; PCC point represents the point of common coupling; PWM represents pulse width modulation; Step 2, based on the PCC point voltage expression without considering the PWM nonlinear link, constructing the PCC point voltage expression considering the PWM nonlinear link in the frequency domain, including: Define the PWM modulation index as a nonlinear function of time variable m(t), which is expressed in the time domain as: （4） where v 载波 (t) is a carrier signal function, v 调制波 (t) is a modulating wave signal function, ΔT represents a non-linear distortion factor reflecting the dead time of the switch, and t represents a time variable. The nonlinear distortion factor ΔT caused by the switching dead time is a dead time adaptive correction term based on the current polarity, which satisfies: （5） Wherein, T dead is a preset dead time, sgn is a sign function, i m represents an m-phase current, and ε is a zero-prevention denominator constant; K comp is a linear constant, reflecting the nonlinear characteristics of the current; Step 3, based on the converter current frequency domain expression without considering the PWM nonlinear link and the PCC point voltage expression considering the PWM nonlinear link in the frequency domain, constructing the grid-connected inverter sequence impedance model considering the PWM nonlinear link, which is used to analyze the impedance regulation capability of renewable energy conversion devices, capture the dynamic behavior of renewable energy generation equipment, and provide analysis tools for grid operation and control, including: The d-axis modulation wave C of the grid-connected inverter in the frequency domain in the synchronous rotating coordinate system is: d and the q-axis modulation wave C is: q ​ （7） wherein C d [ω1] and C q [ω1] represent positive sequence direct-axis and positive sequence quadrature-axis modulation waves of the grid-connected inverter in the synchronous rotating coordinate system, respectively, C d [-ω1] and C q [-ω1] represent negative sequence direct-axis and negative sequence quadrature-axis modulation waves of the grid-connected inverter in the synchronous rotating coordinate system, respectively, C d [0] and C q [0] represent zero sequence direct-axis and zero sequence quadrature-axis modulation waves of the grid-connected inverter in the synchronous rotating coordinate system, respectively; d-axis represents direct-axis, and q-axis represents quadrature-axis; i dr , i qr are reference currents of d-axis and q-axis, respectively, θ PLL is an angle output by a phase-locked loop, H i is a current PI controller, K d is a current feedforward coefficient, K f is a voltage feedforward coefficient; θ i is an angle between a current phasor and d-axis during coordinate transformation; I1, I p , and I n are fundamental current amplitude, positive sequence disturbance current amplitude, and negative sequence disturbance current amplitude, respectively; T PLL (s) is a simplified phase-locked loop transfer function; V p , and V n are positive sequence disturbance voltage amplitude and negative sequence disturbance voltage amplitude, respectively; V1, and φ1 are fundamental voltage amplitude, fundamental angular frequency, and fundamental current initial phase angle, respectively; G v is a transfer function including a sampling link and a low-pass filter, s is a Laplace operator, and j is an imaginary unit; θ i is an angle between a current phasor and d-axis during coordinate transformation, and subscript i represents current.

2. The method of claim 1, wherein the impedance regulation capability of the high renewable energy source penetration power conversion device is analyzed by: The step 1 includes: considering the influence of fundamental voltage, sampling and filtering, phase-locked loop to construct the PCC point voltage expression without considering the PWM nonlinear link.

3. The method of claim 1, wherein the impedance regulation capability of the high renewable energy source penetration power conversion device is analyzed by: The step 1 includes: considering the effect of fundamental current, sampling and filtering, phase-locked function to construct the converter current frequency domain expression without considering the PWM nonlinear link.

4. The method of claim 1, wherein the impedance regulation capability of the high renewable energy source penetration power conversion device is analyzed by: After the time domain nonlinear is equivalent to the frequency domain by using the harmonic linearization theory, when considering the nonlinear effect of the PWM link, the PCC point voltage expression in the synchronous rotating coordinate system in the frequency domain is: （6） wherein V1, and φ1are the fundamental voltage amplitude, the fundamental angular frequency and the fundamental current initial phase angle, respectively; φ vp is the positive sequence disturbance voltage initial phase angle; φ vn is the negative sequence disturbance voltage initial phase angle, V d1 , V q1 is the PCC point voltage frequency domain expression in the synchronous rotating coordinate system without considering the disturbance, V d1 [ω1] and V q1 [ω1] represent the PCC point positive sequence direct-axis voltage and positive sequence quadrature-axis voltage in the synchronous rotating coordinate system, respectively, V d1 [-ω1] and V q1 [-ω1] represent the PCC point negative sequence direct-axis voltage and negative sequence quadrature-axis voltage in the synchronous rotating coordinate system, respectively, V d1 [0] and V q1 [0] represent the PCC point zero sequence direct-axis voltage and zero sequence quadrature-axis voltage in the synchronous rotating coordinate system, respectively, G v is the transfer function containing a sampling link and a low-pass filter, s is the Laplace operator, and j is the imaginary unit; M is the frequency domain expression of the linearized PWM modulation index; and represent the PCC point direct-axis voltage and quadrature-axis voltage in the synchronous rotating coordinate system in the frequency domain, respectively; represents the frequency; H PLL (s) is the transfer function of the phase-locked loop.

5. The method of claim 4, wherein the impedance regulation capability of the high renewable energy source penetration power conversion device is analyzed by: Comprehensive converter current frequency domain expression, formula (5), formula (6), formula (7), the grid-connected inverter sequence impedance model considering the PWM nonlinear link is obtained as: （8） where L f is the inverter filter inductance, V dc is the inverter DC side voltage, V1 is the inverter fundamental voltage amplitude, ω1 is the inverter fundamental angular frequency, K d , K f are the current and voltage feed-forward coefficients, respectively, T PLL (s) is the phase-locked loop transfer function, H PI (s) is the current PI controller transfer function, G i (s) is the current sampling function; represents the positive sequence impedance, represents the negative sequence impedance.

6. The method of claim 5, wherein the impedance regulation capability of the high renewable energy source penetration power conversion device is analyzed by: based on the positive sequence impedance variation ΔZ pdyn and the negative sequence impedance variation ΔZ ndyn dynamically adjusting parameters of the sequence impedance model.

7. The method of claim 6, wherein the impedance regulation capability of the high renewable energy source penetration power conversion device is analyzed by: The adjustment formula is: （9） wherein Z p (k+1) and Z n (k+1) are the (k+1)th iteration positive sequence impedance and negative sequence impedance, respectively, Z p (k) and Z n (k) are the kth iteration positive sequence impedance and negative sequence impedance, respectively, ΔZ pdyn and ΔZ ndyn are the positive sequence impedance variation and negative sequence impedance variation, respectively, K p and K i are the algorithm proportional coefficient and algorithm integral coefficient, respectively, dω is the differential of frequency, and the convergence condition is that the positive sequence impedance and negative sequence impedance of adjacent iterations are located at 50 Hz and the amplitude-frequency characteristic variation is less than 10 -3 .

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