Method for analyzing impedance adjusting capability of high-proportion renewable energy converter device

Abstract

The invention provides an impedance regulation capability analysis method for a high-proportion renewable energy converter device, and belongs to the field of energy, and the method comprises the steps: constructing a PCC point voltage expression and a converter current frequency domain expression which do not consider a PWM (pulse width modulation) nonlinear link; the PCC point represents a common connection point; based on the PCC point voltage expression which does not consider the PWM nonlinear link, constructing a PCC point voltage expression which considers the frequency domain of the PWM nonlinear link; and based on the current frequency domain expression of the converter without considering the PWM nonlinear link and the PCC point voltage expression of the frequency domain of the PWM nonlinear link, constructing a grid-connected inverter sequence impedance model considering the PWM nonlinear link for analyzing the impedance adjustment capability of the renewable energy converter. The dynamic behavior of the renewable energy power generation equipment can be captured, and an analysis tool is provided for power grid operation and control.

Description

Technical Field

[0001] This invention belongs to the field of energy, specifically relating to a method for analyzing the impedance regulation capability of a high-proportion renewable energy converter. Background Technology

[0002] The global energy shortage is becoming increasingly prominent, and human society's demand for renewable energy is constantly increasing. Photovoltaic power generation systems, as an important component of current renewable power generation systems, are widely used throughout the power system due to their environmentally friendly and pollution-free characteristics.

[0003] Photovoltaic (PV) power generation equipment is typically connected to the power grid via power electronic devices, thus its dynamic characteristics and control strategies have a significant impact on grid stability and power quality. Particularly under weak grid conditions, the impedance characteristics of PV equipment have a particularly pronounced effect on system stability. Therefore, accurate modeling of the impedance characteristics of PV equipment is crucial for analyzing and designing its grid-connected control strategies.

[0004] Traditional impedance modeling methods include dq (direct-axis and quadrature-axis) impedance modeling in a synchronously rotating coordinate system and sequence impedance modeling in a stationary natural coordinate system. While 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 neglect the nonlinear and time-varying characteristics of the inverter's dynamic response, resulting in limited model accuracy and applicability. Furthermore, with the increase in renewable energy power generation equipment capacity and changes in grid conditions, traditional modeling methods may fail to adapt to the new operating environment, thus affecting the accuracy of system stability analysis.

[0005] Therefore, there is an urgent need for an improved method for analyzing the impedance regulation capability of high-proportion renewable energy converters to better capture their dynamic characteristics. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for analyzing the impedance regulation capability of high-proportion renewable energy converters. Based on the study of the topology and control methods of photovoltaic power generation equipment, and considering the nonlinear characteristics of the PWM (Pulse Width Modulation) stage, the traditional converter sequence impedance modeling method is improved, enhancing the model's accuracy and applicability. The improved model not only more accurately captures the dynamic behavior of renewable energy power generation equipment but also adapts to different grid conditions, providing a more reliable analytical tool for grid operation and control.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for analyzing the impedance regulation capability of a high-proportion renewable energy converter includes the following steps:

[0009] Step 1: Construct the frequency domain expressions for the PCC point voltage and the converter current without considering the PWM nonlinearity; PCC point represents the point of common connection; PWM represents pulse width modulation.

[0010] 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.

[0011] 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 converters, capture the dynamic behavior of renewable energy power generation equipment, and provide analytical tools for grid operation and control.

[0012] Beneficial effects:

[0013] The impedance regulation capability analysis method for high-proportion renewable energy converters proposed in this invention applies a grid-connected inverter sequence impedance model that considers the nonlinearity of PWM to analyze the impedance regulation capability of renewable energy converters. This method can more accurately capture the dynamic behavior of renewable energy power generation equipment and provide a more reliable analysis tool for grid operation and control. Attached Figure Description

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

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

[0016] Figure 3a , Figure 3b This is a comparison chart of the simulated sequence impedance values ​​obtained from the simulation and the theoretical values ​​obtained from the analysis method proposed in this invention; wherein, Figure 3a This is a comparison chart of positive sequence impedances. Figure 3b This is a comparison chart of negative sequence impedances; Figure 3a of (a) Figure 3b (a) is a comparison chart of amplitudes. Figure 3a (b) Figure 3b (b) is a phase angle comparison diagram;

[0017] Figure 4 This is a flowchart of a method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to the present invention. Detailed Implementation

[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 For grid voltage, i ga i gb i gc V is the grid-connected current of the converter. dc and I dc These represent the DC side voltage and current, respectively.

[0025] The significant nonlinear characteristics exhibited by the converter ports dictate that the core task of impedance modeling lies in linearizing the nonlinear components within the inverter, which is also the main task in the impedance model construction process. By injecting positive and negative sequence disturbance voltages with amplitudes not exceeding 10% of the rated power frequency voltage amplitude into the PCC point, the dynamic characteristics of the converter can be captured without affecting the stable operating point of the system.

[0026] Since the control loop of the grid-connected inverter operates in a synchronous rotating coordinate system, it is necessary to provide equations in the synchronous coordinate system. Ignoring disturbances, the frequency domain expression of the PCC point voltage in the synchronous rotating coordinate system is:

[0027] (1)

[0028] Among them, V1, and These are the fundamental voltage amplitude, fundamental angular frequency, and fundamental current initial phase angle, respectively. The initial phase angle of the positive-sequence disturbance voltage; The initial phase angle of the negative sequence disturbance voltage, V d1 V q1 To express the frequency domain expression of the voltage at point PCC in a synchronously rotating coordinate system without considering disturbances, V d1 [ω1] and V q1 [ω1] represents the positive-sequence direct-axis voltage and positive-sequence quadrature-axis voltage at point PCC in the synchronously rotating coordinate system, respectively. d1 [-ω1] and V q1 [-ω1] represents the negative-sequence direct-axis voltage and negative-sequence quadrature-axis voltage at point PCC in the synchronously rotating coordinate system, respectively. d1 [0] and V q1 [0] represents the zero-sequence direct-axis voltage and zero-sequence quadrature-axis voltage at point PCC in the synchronous rotating coordinate system, respectively. G v It is the transfer function that includes the sampling stage and the low-pass filter, where s is the Laplace operator and j is the imaginary unit. V p V n These represent the positive-sequence disturbance voltage amplitude and the negative-sequence disturbance voltage amplitude, respectively.

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

[0030] (2)

[0031] Among them, H PLL (s) is the transfer function of the phase-locked loop, G v (s) is the transfer function that includes the sampling stage and the low-pass filter.

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

[0033] (3)

[0034] Among them, I1, I p I n These represent the amplitudes of the fundamental current, the positive-sequence disturbance current, and the negative-sequence disturbance current, respectively, θ i This represents the angle between the current phasor and the d-axis during coordinate transformation. The subscript 'i' indicates current; this subscript is used because it represents the angle between the current phasor and the d-axis. G represents the base value of the included angle. i (s) is the current sampling function, T PLL (s) is the phase-locked function defined above. and These represent the positive-sequence direct-axis current and the positive-sequence quadrature-axis current at point PCC in the synchronously rotating coordinate system, respectively. and These represent the negative sequence direct-axis current and the negative sequence quadrature-axis current at point PCC in the synchronously rotating coordinate system, respectively. and These represent the zero-sequence direct-axis current and the zero-sequence quadrature-axis current at point PCC in the synchronous rotating coordinate system, respectively.

[0035] Specifically, step 2 includes:

[0036] When considering the nonlinear characteristics of the pulse width modulation (PWM) stage in a grid-connected inverter, this dynamic process essentially constitutes a nonlinear system with time-varying properties. As a core parameter of the switching device control logic, the PWM modulation index can be defined as a nonlinear function m(t) of the time variable. Its dynamic characteristics are influenced by the combined effects of multiple nonlinear factors, including the time-varying characteristics of the carrier signal, the dynamic fluctuations of the modulation wave component, and the switching dead-zone effect. In time-domain analysis, this nonlinear functional relationship manifests as an unsteady coupling between the modulation parameter and the time variable, and its dynamic response exhibits significant asymmetric harmonic distribution characteristics. The nonlinear function m(t) can be expressed in the time domain as:

[0037] (4)

[0038] Among them, v 载波 (t) is the carrier signal function, v 调制波 (t) is the modulation wave signal function, t is the time variable, and ΔT is the nonlinear distortion factor reflecting the switching dead time, which is an adaptive correction term for the dead time based on the current polarity, satisfying:

[0039] (5)

[0040] Among them, T dead The preset dead time is sgn, where sgn is the sign function, and i m K represents the current in the m-th phase. comp ε is a linear constant that reflects the nonlinear characteristics of the current, and ε is a zero-denominator constant.

[0041] After applying harmonic linearization theory to perform frequency domain equivalent processing on the time-domain nonlinearity, the expression for the PCC point voltage in the synchronous rotating coordinate system in the frequency domain, considering the nonlinear effect of the PWM stage, is as follows: (6)

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

[0043] Specifically, step 3 includes:

[0044] like Figure 2 The diagram shown is a control block diagram of a photovoltaic grid-connected inverter, where i dr i qr Let θ be the reference current for the d-axis and q-axis, respectively. PLL H is the angle output by the phase-locked loop. i For a current PI controller, K d K is the current feedforward coefficient. f This is the voltage feedforward coefficient. The voltage and current in the three-phase (abc) stationary coordinate system are transformed into DC quantities in the dq coordinate system. The current in the dq coordinate system is compared with the given value and then input to the current PI controller. The output of the current PI controller, the voltage feedforward quantity, and the current feedforward quantity are calculated and then transformed again to output the voltage and current in the three-phase stationary coordinate system. After PWM modulation, these will be used as switching signals to control the inverter output.

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

[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 (5), (7), 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 Z nThe amplitude-frequency response change at 50Hz is less than 10. -3 dω is the differential component of frequency, ΔZ pdyn The positive-sequence impedance change, ΔZ ndyn K represents the change in negative sequence impedance. p and K i These are the proportional coefficient and the integral coefficient, respectively.

[0054] Example:

[0055] Establish such in simulation software Figure 1 The simulation model of the grid-connected inverter shown is illustrated in Table 1, with specific parameters as shown in the table.

[0056] Table 1

[0057]

[0058] By injecting positive-sequence or negative-sequence voltage disturbances into the main circuit of a three-phase grid-connected inverter system controlled in a synchronous rotating coordinate system, the sequence impedance of the converter can be monitored. The positive-sequence disturbance voltage injection circuit uses a positive-sequence phase, enabling the simultaneous injection of five positive-sequence voltage signals of different frequencies into the main circuit, thus allowing the checking of the converter's positive-sequence impedance at five different frequency points. Similarly, the negative-sequence disturbance voltage injection circuit uses a negative-sequence phase, enabling the simultaneous injection of five negative-sequence voltage signals of different frequencies into the main circuit, thus allowing the checking of the converter's negative-sequence impedance at five different frequency points. By changing the disturbance voltage frequency and performing cyclic simulations, the positive-sequence or negative-sequence impedance of the converter in multiple frequency bands can be detected.

[0059] The comparison between the simulated sequence impedance values ​​obtained from the simulation and the theoretical values ​​obtained from the analysis method proposed in this invention is shown in the figure below. Figure 3a , Figure 3b As shown, Figure 3a This is a comparison chart of positive sequence impedances. Figure 3b This is a comparison chart of negative sequence impedances. Among them, Figure 3a of (a) Figure 3b (a) is a comparison chart of amplitudes. Figure 3a (b) Figure 3b (b) is a phase angle comparison diagram.

[0060] The comparison shows that the theoretical calculation results and the circuit simulation results are in good agreement. The analysis method proposed in this invention can accurately capture the dynamic behavior of renewable energy power generation equipment, providing a more reliable analysis tool for grid operation and control.

Claims

1. A method for analyzing the impedance regulation capability of a high-proportion renewable energy converter, characterized in that, Includes the following steps: Step 1: Construct the PCC point voltage expression and the converter current frequency domain expression without considering the PWM nonlinearity. PCC stands for Point of Common Connection; PWM stands for Pulse Width Modulation. 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. 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 converters, capture the dynamic behavior of renewable energy power generation equipment, and provide analytical tools for grid operation and control.

2. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 1, characterized in that, Step 1 includes: constructing a PCC point voltage expression that does not consider the PWM nonlinearity, taking into account the influence of fundamental voltage, sampling and filtering, and phase-locked loop.

3. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 1, characterized in that, Step 1 includes: constructing a frequency domain expression for the converter current without considering the effects of the fundamental current, sampling and filtering, and the phase-locked function.

4. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 3, characterized in that, Step 2 includes: Define the PWM modulation index as a nonlinear function m(t) that is a time variable. The nonlinear function m(t) is expressed in the time domain as: （4） Among them, v 载波 (t) is the carrier signal function, v 调制波 (t) is the modulation wave signal function, ΔT represents the nonlinear distortion factor reflecting the switching dead time, and t represents the time variable.

5. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 4, characterized in that, The nonlinear distortion factor ΔT, which reflects the dead time of the switch, is an adaptive dead time correction term based on current polarity, satisfying: （5） Among them, T dead The preset dead time is sgn, where sgn is the sign function, and i m K represents the m-phase current, where ε is the zero-prevention denominator constant; comp ε is a linear constant that reflects the nonlinear characteristics of the current; ε is a zero-denominator constant.

6. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 5, characterized in that, After applying harmonic linearization theory to perform frequency domain equivalent processing on the time-domain nonlinearity, the expression for the PCC point voltage in the synchronous rotating coordinate system in the frequency domain, considering the nonlinear effect of the PWM stage, is as follows: （6） Among them, V1, and These are the fundamental voltage amplitude, fundamental angular frequency, and fundamental current initial phase angle, respectively. The initial phase angle of the positive-sequence disturbance voltage; The initial phase angle of the negative sequence disturbance voltage, V d1 V q1 To express the frequency domain expression of the voltage at point PCC in a synchronously rotating coordinate system without considering disturbances, V d1 [ω1] and V q1 [ω1] represents the positive-sequence direct-axis voltage and positive-sequence quadrature-axis voltage at point PCC in the synchronously rotating coordinate system, respectively. d1 [-ω1] and V q1 [-ω1] represents the negative-sequence direct-axis voltage and negative-sequence quadrature-axis voltage at point PCC in the synchronously rotating coordinate system, respectively. d1 [0] and V q1 [0] represents the zero-sequence direct-axis voltage and zero-sequence quadrature-axis voltage at point PCC in the synchronous rotating coordinate system, respectively. G v It is the transfer function that includes the sampling stage and the low-pass filter, where s is the Laplace operator, j is the imaginary unit, and M is the frequency domain expression of the linearized PWM modulation exponent. and These represent the direct-axis voltage and quadrature-axis voltage of the PCC point in the synchronous rotating coordinate system in the frequency domain, respectively. Indicates frequency; H PLL (s) is the transfer function of the phase-locked loop; V p V n These represent the positive-sequence disturbance voltage amplitude and the negative-sequence disturbance voltage amplitude, respectively.

7. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 6, characterized in that, Step 3 includes: The d-axis modulation wave C of the grid-connected inverter in the synchronous rotating coordinate system in the frequency domain d and q-axis modulated wave C q for: （7） 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; the d-axis represents the direct axis, and the q-axis represents the quadrature axis; i dr i qr Let θ be the reference current along the d-axis and q-axis, respectively. PLL H is the angle output by the phase-locked loop. i For a current PI controller, K d K is the current feedforward coefficient. f θ is the voltage feedforward coefficient; i I1 and I2 are the angles between the current phasors and the d-axis during coordinate transformation. p I n These represent the amplitudes of the fundamental current, the positive-sequence disturbance current, and the negative-sequence disturbance current, respectively; T PLL (s) is the simplified phase-locked loop transfer function.

8. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 7, characterized in that, Combining equations (5), (7), and (8), the sequence impedance model of the grid-connected inverter considering the PWM nonlinearity is obtained as follows: （8） 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 These are the current and voltage feedforward coefficients, T. PLL (s) is the phase-locked loop transfer function, H PI (s) is the transfer function of the current PI controller, G i (s) is the current sampling function; Indicates positive sequence impedance. This represents the negative sequence impedance.

9. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 8, characterized in that, 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.

10. The method for analyzing the impedance regulation capability of a high-proportion renewable energy converter according to claim 9, characterized in that, The formula is adjusted as follows: （9） 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) represents the positive-sequence impedance and negative-sequence impedance of the k-th iteration, respectively, and ΔZ pdyn and ΔZ ndyn These represent the positive-sequence impedance change and the negative-sequence impedance change, respectively, K p and K i These are the algorithm's proportional coefficient and integral coefficient, respectively. dω is the differential component of the frequency. The convergence condition is that the amplitude-frequency characteristic change of the positive-sequence impedance and negative-sequence impedance at 50Hz in adjacent iterations is less than 10. -3 .

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