An impedance modeling method for a hybrid photovoltaic and energy storage power generation system

Abstract

The present invention discloses a method for impedance modeling of a photovoltaic and energy storage hybrid power generation system. By based on a preset control strategy for the photovoltaic power generation unit, an equivalent output impedance model of the photovoltaic power generation unit is established; based on a preset control strategy for the energy storage unit, an equivalent output impedance model of the energy storage unit is established; based on a preset harmonic linearization control strategy, a small-signal coupling model of the AC and DC sides of the photovoltaic and energy storage inverter control unit is established; the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC and DC sides of the photovoltaic and energy storage inverter control unit are fused to construct an impedance model of the photovoltaic and energy storage hybrid power generation system. The present invention considers the coupling effect of the impedance of the photovoltaic and energy storage units on the output impedance characteristics of the photovoltaic and energy storage converter, thereby establishing a more accurate impedance model of the photovoltaic and energy storage power generation system, and is also applicable to the determination of system stability under weak grid conditions, better realizing the application of the impedance model in the photovoltaic and energy storage power generation scenario.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic and energy storage power generation, and particularly discloses a method for impedance modeling of a photovoltaic and energy storage hybrid power generation system. Background Art

[0002] In recent years, with the vigorous development of renewable energy, wind power and photovoltaic power generation have become the main research hotspots. The randomness and volatility of new energy power generation pose a threat to the stable operation of the power grid, while photovoltaic and energy storage hybrid power generation can well suppress the fluctuations of the power grid and participate in the peak regulation and frequency modulation of the power grid. In order to ensure the operation reliability of the new energy system connected to the power grid and reduce the oscillation risk generated by the system, it is particularly necessary to study the operation stability, that is, the impedance characteristics, of the photovoltaic and energy storage system. At present, the research directions of many scholars are as follows: equivalent the capacitor of the photovoltaic and energy storage converter to infinity, ignore the coupling characteristics of the AC and DC sides, and establish its impedance model; or equivalent the photovoltaic and energy storage power generation system to establish an impedance model during stable operation, without considering the influence of the dynamic characteristic changes of the impedance of the photovoltaic array and energy storage battery itself on the output impedance of the photovoltaic and energy storage system.

[0003] The article titled "Modeling of Grid-Connected Inverter Frequency Coupling Characteristics and System Stability Analysis", published in the 39th volume, No. 5 of the Proceedings of the CSEE in 2019, article number: 0258 - 8013(2019), 05 - 1421 - 11, established a grid-connected inverter frequency coupling characteristic model considering factors such as the phase-locked loop, DC voltage loop, and asymmetry of the current control loop. Compared with the previous admittance matrix model, it is more concise and convenient for calculation.

[0004] The article titled "Modeling and Characteristic Analysis of Photovoltaic Power Generation Impedance Considering Photovoltaic Array", published in the Proceedings of the CSEE in 2023, considered the influence of irradiance and temperature on the output impedance of the photovoltaic array, established the impedance model of its photovoltaic power generation system, and revealed the influence of the dynamic characteristics of the photovoltaic array on the AC-side output impedance of photovoltaic power generation.

[0005] To sum up, currently, the influence of considering the impedance characteristics of the photovoltaic and energy storage system on the coupling mechanism of the AC-side impedance characteristics of the photovoltaic and energy storage converter is in a blank, which is of great significance for further research on the stability of the photovoltaic and energy storage system connected to the grid in the future. Summary of the Invention

[0006] The present invention provides a method for impedance modeling of a photovoltaic and energy storage hybrid power generation system, aiming to solve the technical problem that currently, the influence of considering the impedance characteristics of the photovoltaic and energy storage system on the coupling mechanism of the AC-side impedance characteristics of the photovoltaic and energy storage converter is in a blank.

[0007] The present invention relates to a method for impedance modeling of a photovoltaic and energy storage hybrid power generation system, including the following steps:

[0008] Based on a preset control strategy of the photovoltaic power generation unit, establish an equivalent output impedance model of the photovoltaic power generation unit;

[0009] Based on a preset energy storage unit control strategy, an equivalent output impedance model of the energy storage unit is established;

[0010] Based on a preset harmonic linearization control strategy, a small-signal coupling model of the AC and DC sides of the control unit of the photovoltaic energy storage inverter is established;

[0011] The equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC and DC sides of the control unit of the photovoltaic energy storage inverter are fused to construct an impedance model of the photovoltaic energy storage hybrid power generation system.

[0012] Furthermore, in the step of establishing the equivalent output impedance model of the photovoltaic power generation unit based on a preset photovoltaic power generation unit control strategy, the equivalent output impedance model of the photovoltaic power generation unit is:

[0013]

[0014] where Z pv is the equivalent output impedance of the photovoltaic power generation unit, is the small-signal variable of the DC bus voltage, is the small-signal variable of the average current output from the photovoltaic unit to the DC bus, s is the Laplace differential operator, L dc is the boost inductor, G idc is the transfer function of the current control loop, G delay is the digital control delay, v bus is the DC bus voltage, R pv is the equivalent resistance of the photovoltaic unit, i pv is the inductor current, and d is the duty ratio.

[0015] Furthermore, in the step of establishing the equivalent output impedance model of the energy storage unit based on a preset energy storage unit control strategy, the equivalent output impedance model of the energy storage unit is:

[0016]

[0017] where Z bat is the modulus of the equivalent output impedance of the energy storage unit, s is the Laplace differential operator, L dc is the boost inductor, G idc is the transfer function of the current control loop, G delay is the digital delay control, v bus is the DC bus voltage, R bat is the equivalent resistance of the storage battery, i bat is the inductor current, and d is the duty ratio.

[0018] Further, in the step of establishing the small-signal coupling model of the AC and DC sides of the control unit of the photovoltaic-storage inverter based on the preset harmonic linearization control strategy, the small-signal coupling model of the AC and DC sides of the control unit of the photovoltaic-storage inverter is as follows:

[0019]

[0020] Wherein, is the small-signal of the output current of the a-phase of the inverter, is the positive-sequence component of, is the negative-sequence component of, T is the transpose of the matrix, I gp is the amplitude of the positive-sequence component, I gp2 is the amplitude of the positive-sequence component, e is the natural number base in Euler's formula, j is the imaginary unit, is the phase of the positive-sequence component of the current small-signal , is the phase of the negative-sequence component of the current small-signal .

[0021] Further, in the step of fusing the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC and DC sides of the control unit of the photovoltaic-storage inverter to construct the impedance model of the photovoltaic-storage hybrid power generation system, the impedance model of the photovoltaic-storage hybrid power generation system includes the expression of the admittance of the AC port of the photovoltaic-storage inverter considering the output impedance of the photovoltaic-storage hybrid power generation, and the expression of the admittance of the AC port of the photovoltaic-storage inverter is as follows:

[0022]

[0023] Wherein, Y pv is a 2×2 order matrix, Λ 1 is the transfer coefficient between the small-signal of the AC port of the inverter and the small-signal of the current response when the DC bus voltage is constant, Λ 2 is the transfer coefficient between the small-signal of the DC bus voltage and the small-signal of the current response generated by it, P v is the transfer relationship between the small-signal of the AC side voltage and the small-signal of the DC side power, P i is the transfer relationship between the small-signal of the AC side current and the small-signal of the DC side power, I is the 2×2 order identity matrix, F(Z dc ) is the transfer relationship from the small-signal of the DC side power considering the small-signal impedance model of the photovoltaic-storage unit to the small-signal of the DC voltage, Y cfThe filter capacitor is a 2x2 order diagonal matrix, and its expression is Y cf = j2πC f ·diag[f p , f p - 2f 1 .

[0024] Furthermore, in the step of fusing the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC-DC sides of the photovoltaic-storage inverter control unit to construct the impedance model of the photovoltaic-storage hybrid power generation system, the coefficients Λ 1 , Λ 2 are calculated by the following formula:

[0025]

[0026] Among them, Λ 1 is the transfer coefficient between the small-signal of the AC voltage on the inverter side and the small-signal of its current response when the DC bus voltage is constant. K m is the modulation coefficient, V dc is the steady-state component of the DC bus voltage, T PLL (s 1 ) is the PLL transfer function, H gi (s 1 ) is the current controller transfer function, j is the imaginary unit, K gd is the decoupling coefficient, I g1 is the vector expression of the steady-state current, M 1 is the fundamental frequency component represented by the modulation signal, s is the Laplace differential operator, L f is the AC-side inductor, I * g1 is the conjugate of the vector expression of the steady-state current, M 1 * is the conjugate of the fundamental frequency component represented by the modulation signal, s 2 = j2π(f p - 2f 1 ), f p is the perturbation frequency, f 1 is the fundamental wave frequency;

[0027]

[0028] Among them, Λ 2 is the coefficient of the small-signal of the DC bus voltage and the small-signal of the current response, which is mainly related to the voltage outer loop, the current loop, and the PWM modulation ratio; K m is the modulation coefficient, V dcis the DC bus voltage steady-state component, H gi (s 1 ) is the transfer function of the current controller, H vdc (s 1 ) is the transfer function of the voltage controller, M g1 is the fundamental frequency component representing the modulation signal, s = j2πf 1 is, L f is the AC side inductor, j is the imaginary unit, K gd is the decoupling coefficient, M * g1 is the conjugate of the fundamental frequency component representing the modulation signal, s 2 = j2π(f p - 2f 1 ), f p is the perturbation frequency, f 1 is the fundamental wave frequency.

[0029] Furthermore, in the step of fusing the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the AC-DC side small-signal coupling model of the photovoltaic-storage inverter control unit to construct the impedance model of the photovoltaic-storage hybrid power generation system, the coefficients P v and P i are calculated by the following formula:

[0030]

[0031] where, P V is the transfer relationship between the small-signal of the AC side voltage and the small-signal of the DC side power , I ga is the steady-state value of the inverter phase-a output, I * ga is the conjugate of the steady-state value of the inverter phase-a output, P i is the transfer relationship between the small-signal of the AC side current and the small-signal of the DC power, V ga is the steady-state value of the inverter modulation voltage, V * ga is the conjugate of the steady-state value of the inverter modulation voltage, s = j2πf p , s 2 = j2π(f p - 2f 1 ), f p is the perturbation frequency, f 1 is the fundamental wave frequency, L f is the AC side inductor, T is the matrix transpose.

[0032] Further, in the step of constructing the impedance model of the photovoltaic-storage hybrid power generation system by fusing the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC-DC sides of the photovoltaic-storage inverter control unit, the coefficient F(Z dc ) is calculated by the following formula:

[0033]

[0034] where F(Z dc ) is the transfer relationship of the small-signal of the DC-side power considering the impedance of the photovoltaic-storage unit and the DC-bus capacitor to the small-signal of the DC-side voltage, F to the small-signal of the DC-side voltage, F 1 (sC dc ) is the transfer relationship of the impedance of the DC-bus capacitor to the small-signal of the DC-side voltage for the small-signal of the DC-side power, F to the small-signal of the DC-side voltage, F 2 (Z pv ) is the transfer relationship of the photovoltaic unit to the small-signal of the DC-side voltage for the small-signal of the DC-side power, F to the small-signal of the DC-side voltage, F 3 (Z bat ) is the transfer relationship of the energy storage unit to the small-signal of the DC-side voltage for the small-signal of the DC-side power, V to the small-signal of the DC-side voltage, V dc is the steady-state voltage of the DC bus, Z pv is the equivalent output impedance of the photovoltaic power generation unit, Z bat is the equivalent output impedance of the energy storage power generation unit, s 1 =j2π(f p -f 1 ) where f p is the perturbation frequency, f 1 is the fundamental frequency, C dc is the DC bus capacitor, I dc is the steady-state current of the DC bus, V dc is the steady-state voltage of the DC bus.

[0035] The beneficial effects achieved by the present invention are:

[0036] The present invention provides a method for impedance modeling of a photovoltaic-storage hybrid power generation system. By based on a preset control strategy for a photovoltaic power generation unit, an equivalent output impedance model of the photovoltaic power generation unit is established; based on a preset control strategy for a energy storage unit, an equivalent output impedance model of the energy storage unit is established; based on a preset harmonic linearization control strategy, a small-signal coupling model of the AC and DC sides of the photovoltaic-storage inverter control unit is established; the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC and DC sides of the photovoltaic-storage inverter control unit are integrated to construct an impedance model of the photovoltaic-storage hybrid power generation system. The method for impedance modeling of the photovoltaic-storage hybrid power generation system provided by the present invention considers the coupling effect of the impedances of the photovoltaic and energy storage units on the output impedance characteristics of the photovoltaic-storage converter, thereby establishing a more accurate impedance model of the photovoltaic-storage power generation system. At the same time, it is also applicable to the determination of system stability under weak grid conditions, and better realizes the application of the impedance model in the photovoltaic-storage power generation scenario. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic flow chart of the method for impedance modeling of the photovoltaic-storage hybrid power generation system of the present invention;

[0038] Figure 2 is a schematic diagram of the control strategy of the photovoltaic power generation unit of the present invention;

[0039] Figure 3 is a schematic diagram of the control strategy of the energy storage unit of the present invention;

[0040] Figure 4 is a schematic diagram of the photovoltaic-storage inverter control unit of the present invention;

[0041] Figure 5 is a schematic diagram of the topological structure of the photovoltaic-storage system of the present invention;

[0042] Figure 6 is a small-signal transfer relationship diagram of the photovoltaic-storage power generation system of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0044] As Figure 1 shown, the present invention proposes a method for impedance modeling of a photovoltaic-storage hybrid power generation system, including the following steps:

[0045] Step S100: Based on a preset control strategy for a photovoltaic power generation unit, establish an equivalent output impedance model of the photovoltaic power generation unit.

[0046] Please see Figures 2 to 5, adopt the control strategy of MPPT (Maximum Power Point Tracking) maximum power tracking to establish an equivalent output impedance model of the photovoltaic power generation unit.

[0047] Step S200: Based on the preset energy storage unit control strategy, establish an equivalent output impedance model of the energy storage unit.

[0048] Equivalent the battery to a voltage source, and respectively consider the internal resistances of the photovoltaic and the battery (without considering the influence of factors such as temperature, light, and battery aging). Use the small-signal method to establish the equivalent output impedance models of the photovoltaic and energy storage units from the DC bus terminal.

[0049] Step S300: Based on the preset harmonic linearization control strategy, establish a small-signal coupling model of the AC and DC sides of the photovoltaic energy storage inverter control unit.

[0050] Adopt the harmonic linearization method to establish a small-signal coupling model of the AC and DC sides of the photovoltaic energy storage converter. Superimpose a small-signal perturbation on the steady-state operating point of the system grid voltage to establish a frequency-domain linearized impedance model. The photovoltaic energy storage inverter control unit uses multi-harmonic linearization modeling.

[0051] The photovoltaic energy storage model adopts a common bus topology structure and control strategy. The BOOST boost circuits adopted by the photovoltaic unit and the energy storage unit are basically the same, but the internal resistances of the photovoltaic and energy storage units are different. R pv and R bat respectively represent the equivalent resistances in the photovoltaic system battery (without considering influencing factors such as temperature, light, and battery aging). e pv and v bat are the electromotive forces in the photovoltaic system and the battery respectively. i pv and i bat are the inductor currents, i pvbus and i batbus are the average values of the currents flowing into the DC bus within one cycle of the photovoltaic and energy storage units. V pv is the voltage at the photovoltaic power generation port. G vdc , G idc both adopt PI (Proportional Integral) control, and G delay (s) is the control delay link generated by PMW (Pulse Width Modulation) control.

[0052] Step S400: Integrate the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC and DC sides of the photovoltaic energy storage inverter control unit to construct an impedance model of the photovoltaic energy storage hybrid power generation system.

[0053] Fuse the established equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC and DC sides of the photovoltaic energy storage inverter control unit to construct a common bus topology of the impedance model of the photovoltaic energy storage hybrid power generation system.

[0054] The impedance model of the photovoltaic energy storage hybrid power generation system adopts a system topology structure, which includes three parts: photovoltaic power generation, energy storage, and grid-connected converter. Among them, v a 、v b 、v c are the grid connection point voltages, i ga 、i gb 、i gc are the currents at the output end of the grid-connected converter, i ca 、i cb 、i cc are the three-phase filter capacitor voltages, L f and C f are the filter inductor and capacitor. θ PLL is the phase angle collected by the phase-locked loop at the grid connection point voltage, V dcref is the DC bus voltage command value, which is provided by the photovoltaic MPPT algorithm and the energy storage battery BMS (Battery Management System). v d 、v q ,i d 、i q are the d-axis and q-axis voltage and current respectively, H gi (s), H vdc (s) are the transfer functions of the PI controllers of the current inner loop and the DC voltage outer loop respectively, i dref 、i qref are the d-axis and q-axis reference currents obtained by the DC bus voltage outer loop PI controller respectively. K gd is the current loop decoupling coefficient.

[0055] Furthermore, in the impedance modeling method of the photovoltaic energy storage hybrid power generation system proposed in this embodiment, in step S100, in the equivalent output impedance model of the photovoltaic power generation unit, it is assumed that the internal resistance R pv of the photovoltaic power generation is a fixed value, and the influence of non-linear changes caused by external factors such as temperature and light is not considered. The equivalent impedance of the photovoltaic unit is obtained by the small-signal method as:

[0056]

[0057] In formula (1), Z pv is the equivalent output impedance of the photovoltaic power generation unit, is the small-signal variable of the DC bus voltage, is the small-signal variable of the average current output from the photovoltaic unit to the DC bus, and s is the Laplace differential operator, Ldc is the boost inductor, G idc is the transfer function of the current control loop, G delay is the digital control delay, v bus is the DC bus voltage, R pv is the equivalent resistance of the photovoltaic unit, i pv is the inductor current, and d is the duty cycle.

[0058] Preferably, in the impedance modeling method of the photovoltaic and energy storage hybrid power generation system proposed in this embodiment, in step S200, similarly, R bat is the equivalent output impedance model of the energy storage unit established by assuming that the internal resistance of the battery is a fixed value without considering the influence of factors such as battery temperature and aging:

[0059]

[0060] In formula (2), Z bat is the modulus of the equivalent output impedance of the energy storage unit, s is the Laplace differential operator, L dc is the boost inductor, G idc is the transfer function of the current control loop, G delay is the digital delay control, v bus is the DC bus voltage, R bat is the equivalent resistance of the battery, i bat is the inductor current, and d is the duty cycle.

[0061] Furthermore, in the impedance modeling method of the photovoltaic and energy storage hybrid power generation system proposed in this embodiment, in step S300, the small-signal coupling model of the AC and DC sides of the photovoltaic and energy storage converter is established by the harmonic linearization method. A small-signal perturbation is superimposed on the steady-state operating point of the system grid voltage to establish a frequency-domain linearized impedance model. The inverter unit of the photovoltaic and energy storage converter adopts multi-harmonic linearization modeling. The steady-state values and small-signal models of the AC and DC side voltages and currents of the photovoltaic and energy storage converter are defined as follows:

[0062]

[0063] In formula (3), V a is the steady-state value of the grid-connected phase-a voltage, V 1 is the vector value of the fundamental voltage; V 1 * is the conjugate of the vector value of the fundamental voltage; e is the natural number base in Euler's formula; j is the complex operator; is the phase of the fundamental voltage.

[0064]

[0065] In formula (4), I ga is the steady-state value of the grid-connected phase-a current, I g1is the vector value of the fundamental current wave; I g1 * is the conjugate of the vector value of the fundamental current wave; e is the base of the natural logarithm in Euler's formula; j is the complex operator; is the phase of the fundamental current wave.

[0066]

[0067] In formula (5), is the small-signal of the grid-connected point a-phase voltage, is positive-sequence component;

[0068] is negative-sequence component; T is the transpose of the matrix; V p is the amplitude of the positive-sequence component of the small-signal of the grid-connected point a-phase voltage; e is the base of the natural logarithm in Euler's formula; j is the imaginary unit; is the positive-sequence component of the small-signal current of p2 is the negative-sequence component of the small-signal of the grid-connected point a-phase voltage of is the negative-sequence component of the small-signal current of

[0069]

[0070] In formula (6), is the small-signal of the inverter a-phase output current, is positive-sequence component, is negative-sequence component, T is the transpose of the matrix, I gp is the amplitude of the positive-sequence component, I gp2 is the amplitude of the positive-sequence component, e is the base of the natural logarithm in Euler's formula, j is the imaginary unit, is the positive-sequence component of the small-signal current of is the negative-sequence component of the small-signal current of dc , I dc are the steady-state values of the voltage and current on the DC side of the PV energy storage inverter; —the small-signals of the voltage and current on the DC side of the PV energy storage inverter.

[0071] Superimpose a positive-sequence voltage perturbation small-signal at the steady-state operating point of the PV energy storage system grid connection with a frequency of f p , according to the superposition principle of linear circuits, the small-signal current at the output of the PV energy storage inverter Is the output small-signal current of the inverter when the DC bus voltage is constant And the small-signal current generated when the DC bus voltage fluctuates The sum. When the change in the DC bus voltage is not considered, the voltage small-signal After passing through the phase-locked loop, the current inner-loop controller, and PWM modulation, the output small-current signal is And The transfer function between is represented by Λ 1 The small-signal current output on the AC side And Generate active power fluctuations. According to the principle of AC-DC power balance, the DC side generates a DC power small-signal And the voltage small-signal And the current small-signal The transfer coefficients between are P V And P i The DC power small-signal Further affects the AC voltage small-signal And the AC current small-signal The transfer relationships are represented by P v And P i When the DC side impedance is only composed of the DC bus capacitor C dc The impedance transfer relationship between the DC power small-signal And the DC voltage small-signal Is F 1 (sC dc ) If the output impedance characteristics of photovoltaic power generation and battery power generation are considered and are all in parallel with the DC bus capacitor, then its transfer relationship is simplified to F 2 (Z pv ) + F 3 (Z bat ) The DC voltage small-signal After passing through the DC voltage outer loop and current loop decoupling, and then through PWM modulation, the current small-signal The transfer function of the AC output port is represented by Λ 2 Is represented.

[0072] Preferably, see Figures 1 to 6 In this embodiment, the impedance modeling method of the photovoltaic and energy storage hybrid power generation system is proposed. In step S400, the impedance model of the photovoltaic and energy storage hybrid power generation system includes an expression of the admittance of the AC port of the photovoltaic and energy storage inverter considering the output impedance of the photovoltaic and energy storage hybrid power generation. The expression of the admittance of the AC port of the photovoltaic and energy storage inverter is:

[0073]

[0074] In formula (7), Y pv Is a 2*2 order matrix, Λ 1For the small-signal of the inverter AC port when the DC bus voltage is constant and the small-signal of the current response between the transfer coefficient, Λ 2 is the small-signal of the DC bus voltage and the small-signal of the current response generated by it the transfer coefficient of, P v is the transfer relationship between the small-signal of the AC-side voltage and the small-signal of the DC-side power of, P i is the transfer relationship between the small-signal of the AC-side current and the small-signal of the DC-side power of, I is the 2×2 identity matrix, F(Z dc ) is the small-signal of the DC-side power considering the small-signal impedance model of the PV storage unit to the small-signal of the DC voltage of, Y cf is the 2×2 diagonal matrix of the filter capacitor, and the expression is Y cf = j2πC f ·diag[f p , f p -2f 1 .

[0075] The coefficient Λ 1 、Λ 2 is calculated by the following formula:

[0076]

[0077] In formula (8), Λ 1 is the transfer coefficient between the small-signal of the AC voltage on the inverter side and the small-signal of its current response when the DC bus voltage is constant and the small-signal of its current response between, K m is the modulation coefficient, V dc is the steady-state component of the DC bus voltage, T PLL (s 1 ) is the transfer function of the phase-locked loop, H gi (s 1 ) is the transfer function of the current controller, j is the imaginary unit, K gd is the decoupling coefficient, I g1 is the vector expression of the steady-state current, M 1 is the fundamental frequency component represented by the modulation signal, s is the Laplace differential operator, L f is the AC-side inductor, I * g1 is the conjugate of the vector expression of the steady-state current, M 1 * is the conjugate of the fundamental frequency component represented by the modulation signal, s 2 = j2π(fp -2f 1 ), where f p is the disturbance frequency, and f 1 is the fundamental frequency;

[0078]

[0079] In Equation (9), Λ 2 is the coefficient of the small-signal of the DC bus voltage and the small-signal of the current response, which is mainly related to the outer voltage loop, the current loop, and the PWM modulation ratio; K m is the modulation coefficient, V dc is the steady-state component of the DC bus voltage, H gi (s 1 ) is the transfer function of the current controller, H vdc (s 1 ) is the transfer function of the voltage controller, M g1 is the fundamental frequency component representing the modulation signal, s = j2πf 1 is, L f is the AC-side inductor, j is the imaginary unit, K gd is the decoupling coefficient, M * g1 is the conjugate of the fundamental frequency component representing the modulation signal, s 2 = j2π(f p -2f 1 ), where f p is the disturbance frequency, and f 1 is the fundamental frequency.

[0080] It is obtained from the active power balance equation of the AC and DC sides of the photovoltaic energy storage converter: Solved according to the model:

[0081]

[0082] In Equation (10), P V is the transfer relationship between the small-signal of the AC-side voltage and the small-signal of the DC-side power , I ga is the steady-state value of the output of the inverter's phase a, I * ga is the conjugate of the steady-state value of the output of the inverter's phase a, P i is the transfer relationship between the small-signal of the AC-side current and the small-signal of the DC power, V ga is the steady-state value of the modulation voltage of the inverter, V * ga is the conjugate of the steady-state value of the modulation voltage of the inverter, s = j2πf p , s 2 = j2π(f p -2f1 ), where f p is the disturbance frequency, f 1 is the fundamental frequency, L f is the AC-side inductor, and T is the matrix transpose.

[0083] The coefficient F(Z dc ) represents the transfer relationship between the DC power small signal and the DC voltage small signal . Write the DC power small signal equation at the steady-state operating point of the DC bus capacitor:

[0084]

[0085] In formula (11), is the DC-side power small signal, V dc and I dc are the steady-state values of the DC voltage and current, respectively, is the DC current small signal, expressed as is the DC voltage small signal; Z dc is the impedance of the power generation side considering the photovoltaic energy storage and the DC bus capacitor.

[0086] The DC power small signal equation can be transformed into:

[0087]

[0088] In formula (12), is the DC-side power small signal, V dc and I dc are the steady-state values of the DC voltage and current, respectively, represents the reciprocal of the DC-side small-signal impedance, is the reciprocal of the DC-side steady-state impedance, is the DC bus voltage small signal.

[0089] The DC-side impedance is composed of the parallel connection of the DC bus capacitor, the photovoltaic unit, and the energy storage unit impedance, and can be expressed as:

[0090]

[0091] In formula (13), F(Z dc ) is the transfer relationship from the DC-side power small signal considering the photovoltaic energy storage unit and the DC bus capacitor impedance to the DC-side voltage small signal , F 1 (sC dc ) is the transfer relationship of the DC bus capacitor impedance from the DC-side power small signal to the DC-side voltage small signal , F2 (Z pv ) is the transfer relationship from the small-signal power on the DC side of the photovoltaic unit to the small-signal DC side voltage . F 3 (Z bat ) is the transfer relationship from the small-signal power on the DC side of the energy storage unit to the small-signal DC side voltage . V dc is the steady-state voltage of the DC bus capacitor, Z pv is the equivalent output impedance of the photovoltaic power generation unit, Z bat is the equivalent output impedance of the energy storage power generation unit, s 1 = j2π(f p - f 1 ), f p is the perturbation frequency, f 1 is the fundamental frequency, C dc is the DC bus capacitor, I dc is the steady-state current of the DC bus, V dc is the steady-state voltage of the DC bus.

[0092] Compared with the prior art, the impedance modeling method of the photovoltaic and energy storage hybrid power generation system provided in this embodiment establishes an equivalent output impedance model of the photovoltaic power generation unit based on a preset control strategy of the photovoltaic power generation unit; establishes an equivalent output impedance model of the energy storage unit based on a preset control strategy of the energy storage unit; establishes a small-signal coupling model of the AC and DC sides of the photovoltaic and energy storage inverter control unit based on a preset harmonic linearization control strategy; fuses the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC and DC sides of the photovoltaic and energy storage inverter control unit to construct an impedance model of the photovoltaic and energy storage hybrid power generation system. The impedance modeling method of the photovoltaic and energy storage hybrid power generation system provided in this embodiment considers the coupling effect of the impedances of the photovoltaic and energy storage units on the output impedance characteristics of the photovoltaic and energy storage converter, thereby establishing a more accurate impedance model of the photovoltaic and energy storage power generation system, and is also applicable to the determination of system stability under weak grid conditions, and better realizes the application of the impedance model in the photovoltaic and energy storage power generation scenarios.

[0093] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A method for impedance modeling of a photovoltaic and energy storage hybrid power generation system, characterized in that, it includes the following steps: Based on a preset control strategy for a photovoltaic power generation unit, establish an equivalent output impedance model of the photovoltaic power generation unit; Based on a preset control strategy for an energy storage unit, establish an equivalent output impedance model of the energy storage unit; Based on a preset harmonic linearization control strategy, establish a small-signal coupling model for the AC and DC sides of the control unit of the photovoltaic and energy storage inverter; Fuse the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model for the AC and DC sides of the control unit of the photovoltaic and energy storage inverter to construct an impedance model of the photovoltaic and energy storage hybrid power generation system; In the step of establishing an equivalent output impedance model of the photovoltaic power generation unit based on a preset control strategy for the photovoltaic power generation unit, the equivalent output impedance model of the photovoltaic power generation unit is: Among them, Z pv is the equivalent output impedance of the photovoltaic power generation unit, is the small-signal variable of the DC bus voltage, is the small-signal variable of the average current output from the photovoltaic unit to the DC bus, s is the Laplace differential operator, L dc is the boost inductor, G idc is the transfer function of the current control loop, G delay is the digital control delay, v bus is the DC bus voltage, R pv is the equivalent resistance of the photovoltaic unit, i pv is the inductor current, d is the duty cycle; In the step of establishing an equivalent output impedance model of the energy storage unit based on a preset control strategy for the energy storage unit, the equivalent output impedance model of the energy storage unit is: Among them, Z bat is the modulus of the equivalent output impedance of the energy storage unit, s is the Laplace differential operator, and L dc is the boost inductor, G idc is the transfer function of the current control loop, G delay is the digital delay control, v bus is the DC bus voltage, R bat is the equivalent resistance of the battery, i bat is the inductor current, and d is the duty cycle; In the step of establishing a small-signal coupling model for the AC and DC sides of the control unit of the photovoltaic and energy storage inverter based on a preset harmonic linearization control strategy, the small-signal coupling model for the AC and DC sides of the control unit of the photovoltaic and energy storage inverter is: Among them, is the small-signal output current of the a-phase of the inverter, is the positive-sequence component of, is the negative-sequence component of, T is the transpose of the matrix, I gp is the amplitude of the positive-sequence component, I gp2 is the amplitude of the positive-sequence component, e is the natural number base in Euler's formula, j is the imaginary unit, is the positive-sequence component of the current small signal of the phase, is the negative-sequence component of the current small signal of the phase; In the step of fusing the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model for the AC and DC sides of the control unit of the photovoltaic and energy storage inverter to construct an impedance model of the photovoltaic and energy storage hybrid power generation system, the impedance model of the photovoltaic and energy storage hybrid power generation system includes an expression for the admittance of the AC port of the photovoltaic and energy storage inverter considering the output impedance of the photovoltaic and energy storage hybrid power generation, and the expression for the admittance of the AC port of the photovoltaic and energy storage inverter is: Among them, Y pv is a 2×2 matrix, Λ 1 is the transfer coefficient between the small-signal of the AC port of the inverter and the small-signal of the current response when the DC bus voltage is constant, Λ 2 is the transfer coefficient between the small-signal of the DC bus voltage and the small-signal of the current response it generates, P v is the transfer relationship between the small-signal of the AC-side voltage and the small-signal of the DC-side power, P i is the transfer relationship between the small-signal of the AC-side current and the small-signal of the DC-side power, I is the 2×2 identity matrix, F(Z dc ) is the transfer relationship from the small-signal of the DC-side power considering the small-signal impedance model of the photovoltaic and energy storage unit to the small-signal of the DC voltage, Y cf is a 2×2 diagonal matrix of the filter capacitor.

2. The method for impedance modeling of a photovoltaic and energy storage hybrid power generation system according to claim 1, characterized in that, In the step of constructing the impedance model of the photovoltaic-storage hybrid power generation system by fusing the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the small-signal coupling model of the AC and DC sides of the photovoltaic-storage inverter control unit, the coefficients Λ 1 , Λ 2 are calculated by the following formula: Among them, Λ 1 is the transfer coefficient between the small-signal of the AC voltage on the inverter side and the small-signal of its current response when the DC bus voltage is constant, K is the small-signal of the AC voltage on the inverter side, and its current response small-signal is the transfer coefficient between them, K m is the modulation coefficient, V dc is the steady-state value of the DC bus voltage, T PLL (s 1 ) is the transfer function of the phase-locked loop, H gi (s 1 ) is the transfer function of the current controller, j is the imaginary unit, K gd is the decoupling coefficient, I g1 is the vector expression of the steady-state current, M 1 is the fundamental frequency component represented by the modulation signal, s is the Laplace differential operator, L f is the AC side inductor, I * g1 is the conjugate of the vector of the steady-state current, M 1 * is the conjugate of the fundamental frequency component represented by the modulation signal, s 2 = j2π(f p - 2f 1 ), f p is the perturbation frequency, f 1 is the fundamental wave frequency; Among them, Λ 2 is the small-signal of the current bus voltage and the small-signal of the current response The coefficient is mainly related to the voltage outer loop, the current loop and the PWM modulation ratio; K m is the modulation coefficient, V dc is the steady-state value of the DC bus voltage, H gi (s 1 ) is the transfer function of the current controller, H vdc (s 1 ) is the transfer function of the voltage controller, M g1 is the fundamental frequency component representing the modulation signal, L f is the AC side inductor, j is the imaginary unit, K gd is the decoupling coefficient, M * g1 is the conjugate of the fundamental frequency component representing the modulation signal, s = j2πf 1 , s 2 = j2π(f p - 2f 1 ), f p is the disturbance frequency, f 1 is the fundamental wave frequency.

3. The method for impedance modeling of a photovoltaic and energy storage hybrid power generation system according to claim 1, characterized in that, In the step of constructing the impedance model of the photovoltaic-storage hybrid power generation system by fusing the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the AC-DC side small-signal coupling model of the photovoltaic-storage inverter control unit, the coefficients P v and P i are calculated by the following formula: Among them, P V is the transfer relationship between the AC-side voltage small signal and the DC-side power small signal , I ga is the steady-state value of the a-phase output of the inverter, I * ga is the conjugate of the steady-state value of the a-phase output of the inverter, P i is the transfer relationship between the AC-side current small signal and the DC power small signal, V ga is the steady-state value of the inverter modulation voltage, V * ga is the conjugate of the steady-state value of the inverter modulation voltage, s = j2πf p , s 2 = j2π(f p - 2f 1 ), f p is the perturbation frequency, f 1 is the fundamental frequency, L f is the AC-side inductor, and T is the matrix transpose.

4. The method for impedance modeling of a photovoltaic and energy storage hybrid power generation system according to claim 1, characterized in that, In the step of constructing the impedance model of the photovoltaic and energy storage hybrid power generation system by integrating the equivalent output impedance model of the photovoltaic power generation unit, the equivalent output impedance model of the energy storage unit, and the AC-DC side small-signal coupling model of the photovoltaic and energy storage inverter control unit, the coefficient F(Z dc ) is calculated by the following formula: Among them, F(Z dc ) is the transfer relationship of the small-signal DC-side power considering the impedance of the photovoltaic-storage unit and the DC-bus capacitor from the small-signal DC-side power to the small-signal DC-side voltage . F 1 (sC dc ) is the transfer relationship of the DC-bus capacitor impedance from the small-signal DC-side power to the small-signal DC-side voltage . F 2 (Z pv ) is the transfer relationship of the photovoltaic unit from the small-signal DC-side power to the small-signal DC-side voltage . F 3 (Z bat ) is the transfer relationship of the energy storage unit from the small-signal DC-side power to the small-signal DC-side voltage . V dc is the steady-state voltage of the DC bus, Z pv is the equivalent output impedance of the photovoltaic power generation unit, Z bat is the equivalent output impedance of the energy storage power generation unit, s 1 =j2π(f p -f 1 ), f p is the perturbation frequency, f 1 is the fundamental frequency, C dc is the DC bus capacitor, I dc is the steady-state current of the DC bus, V dc is the steady-state voltage of the DC bus.

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