Method and device for determining impedance model of grid-connected inverter

Abstract

The embodiment of the invention discloses a method and a device for determining a mixed impedance model of a grid-connected inverter. The method for determining the hybrid impedance model of the grid-connected inverter comprises the following steps: determining a basic mathematical model and a hybrid small signal model of the grid-connected inverter according to grid-connected parameters and grid-connected structure information; determining a small signal impedance model of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters, and determining a continuous impedance model of the grid-connected inverter according to the small signal impedance model; determining a mixed small signal model of the grid-connected inverter based on the discrete characteristics of a control system of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters, and determining a mixed impedance model of the grid-connected inverter according to the mixed small signal model; and determining a target impedance model according to the continuous impedance model and the mixed impedance model. According to the technical scheme provided by the embodiment of the invention, the accuracy of the impedance model can be ensured, and the stability analysis on an actual grid-connected system is facilitated.

Description

Technical Field

[0001] Embodiments of the present invention relate to the technology of grid-connected inverters, and in particular, to a method and device for determining an impedance model of a grid-connected inverter. Background Art

[0002] The existence of high grid impedance and the negative impact of the phase-locked loop under a weak grid lead to resonance phenomena when the inverter is grid-connected. To analyze the stability problem of the grid-connected inverter, it is necessary to determine the impedance model of the grid-connected inverter. However, the traditional method for determining the impedance model of the grid-connected inverter has a problem of poor accuracy when analyzing the oscillatory instability state of the grid-connected inverter under a weak grid. Summary of the Invention

[0003] Embodiments of the present invention provide a method and device for determining an impedance model of a grid-connected inverter to ensure the accuracy of the impedance model and facilitate the stability analysis of the actual grid-connected system.

[0004] In a first aspect, embodiments of the present invention provide a method for determining an impedance model of a grid-connected inverter, including:

[0005] Obtaining the grid-connected parameters and grid-connected structure information of the grid-connected inverter;

[0006] Determining the basic mathematical model of the grid-connected inverter according to the grid-connected parameters and grid-connected structure information;

[0007] Determining the hybrid small-signal model of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters, and based on the discrete characteristics of the control system of the grid-connected inverter, and determining the hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model;

[0008] Determining the target impedance model according to the continuous impedance model and the hybrid impedance model.

[0009] Optionally, the determining the hybrid small-signal model according to the basic mathematical model and the grid-connected parameters, and based on the discrete characteristics of the control system of the grid-connected inverter, includes:

[0010] Sampling the continuous output voltage and output current of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters, and based on the discrete characteristics of the control system of the grid-connected inverter, to obtain the discretized output voltage and output current;

[0011] Establishing the hybrid small-signal model according to the discretized output voltage and output current.

[0012] Optionally, the determining the hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model includes:

[0013] According to the hybrid small-signal model, an equivalent hybrid small-signal circuit is determined; the equivalent hybrid small-signal circuit is a circuit including an inverter side and a grid side;

[0014] According to the equivalent hybrid small-signal circuit, the equivalent impedance of the grid-connected inverter is determined to determine the hybrid impedance model.

[0015] Optionally, the determining of the equivalent hybrid small-signal circuit according to the hybrid small-signal model includes:

[0016] According to the hybrid small-signal model, the output voltage and output current of the hybrid small-signal model are determined;

[0017] According to the output voltage and output current of the hybrid small-signal model, the equivalent hybrid small-signal circuit is determined.

[0018] Optionally, the hybrid impedance model wherein, is the equivalent impedance, and are respectively two parallel impedances on the inverter side of the equivalent hybrid small-signal circuit.

[0019] Optionally, the determining of the target impedance model according to the continuous impedance model and the hybrid impedance model includes:

[0020] Based on the hybrid impedance model and the continuous impedance model, a stability analysis of the grid-connected inverter is performed;

[0021] If the grid-connected inverter is unstable during operation, and the grid-connected inverter is unstable based on the hybrid impedance model and stable based on the continuous impedance model, then the target impedance model is determined to be the hybrid impedance model.

[0022] Optionally, the determining of the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and the grid connection parameters includes:

[0023] According to the basic mathematical model and the grid connection parameters, the transfer function between the grid-connected voltage disturbance and the grid-connected current disturbance of the grid-connected inverter is determined;

[0024] According to the basic mathematical model and the transfer function, the small-signal impedance model of the grid-connected inverter is determined.

[0025] Optionally, the determining of the continuous impedance model of the grid-connected inverter according to the small-signal impedance model includes:

[0026] According to the small-signal impedance model, the output current disturbance of the grid-connected inverter is determined;

[0027] Determine an equivalent small-signal circuit according to the small-signal impedance model and the output current perturbation; the equivalent small-signal circuit is a circuit including an inverter side and a grid side;

[0028] Determine the equivalent impedance of the grid-connected inverter according to the equivalent small-signal circuit to determine the continuous impedance model.

[0029] Optionally, there is a functional relationship between the output voltage and the output current of the hybrid small-signal model.

[0030] In a second aspect, an embodiment of the present invention provides an impedance model determination device for a grid-connected inverter, including:

[0031] A parameter acquisition module for acquiring grid connection parameters and grid connection structure information of the grid-connected inverter;

[0032] A basic model determination module for determining a basic mathematical model of the grid-connected inverter according to the grid connection parameters and the grid connection structure information;

[0033] A continuous model determination module for determining a small-signal impedance model of the grid-connected inverter according to the basic mathematical model and the grid connection parameters, and determining a continuous impedance model of the grid-connected inverter according to the small-signal impedance model;

[0034] A hybrid model determination module for determining a hybrid small-signal model of the grid-connected inverter according to the basic mathematical model and the grid connection parameters and based on the discrete characteristics of the control system of the grid-connected inverter, and determining a hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model;

[0035] A target model determination module for determining a target impedance model according to the continuous impedance model and the hybrid impedance model.

[0036] The impedance model determination method and device for a grid-connected inverter provided by an embodiment of the present invention. The impedance model determination method for a grid-connected inverter includes: obtaining the grid-connection parameters and grid-connection structure information of the grid-connected inverter; determining the basic mathematical model of the grid-connected inverter according to the grid-connection parameters and grid-connection structure information; determining the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and grid-connection parameters, and determining the continuous impedance model of the grid-connected inverter according to the small-signal impedance model; determining the hybrid small-signal model of the grid-connected inverter according to the basic mathematical model and grid-connection parameters and based on the discrete characteristics of the control system of the grid-connected inverter, and determining the hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model; determining the target impedance model according to the continuous impedance model and the hybrid impedance model. The impedance model determination method and device for a grid-connected inverter provided by an embodiment of the present invention determine the target impedance model according to the continuous impedance model and the hybrid impedance model. Specifically, stability analysis is performed on the grid-connected inverter based on the hybrid impedance model and the continuous impedance model. If the grid-connected inverter operates unstably based on the hybrid impedance model and stably based on the continuous impedance model, and the actually operating grid-connected inverter is in an unstable state, then the analysis of the hybrid impedance model is correct and the analysis of the continuous impedance model is incorrect. The target impedance model is determined as the hybrid impedance model to ensure the accuracy of the impedance model and facilitate the stability analysis of the actual grid-connected system. Description of the Drawings

[0037] Figure 1 is a flowchart of a method for determining the impedance model of a grid-connected inverter provided in Embodiment 1 of the present invention;

[0038] Figure 2 is a schematic diagram of a grid-connected inverter provided in Embodiment 1 of the present invention;

[0039] Figure 3 is a schematic diagram of the control structure of a grid-connected inverter provided in Embodiment 1 of the present invention;

[0040] Figure 4 is a schematic diagram of the basic mathematical model of a grid-connected inverter provided in Embodiment 1 of the present invention;

[0041] Figure 5 is a schematic diagram of the small-signal impedance model of a grid-connected inverter provided in Embodiment 1 of the present invention;

[0042] Figure 6 is a schematic diagram of the equivalent small-signal circuit of a grid-connected inverter provided in Embodiment 1 of the present invention;

[0043] Figure 7 is a flowchart of a method for determining the impedance model of a grid-connected inverter provided in Embodiment 2 of the present invention;

[0044] Figure 8It is a schematic diagram of a hybrid structure of a grid-connected inverter provided in Embodiment 2 of the present invention;

[0045] Figure 9 It is a schematic diagram of a hybrid small-signal model of a grid-connected inverter provided in Embodiment 2 of the present invention;

[0046] Figure 10 It is a schematic diagram of an equivalent hybrid small-signal circuit of a grid-connected inverter provided in Embodiment 2 of the present invention;

[0047] Figure 11 It is a schematic diagram of a grid-connected current provided in Embodiment 2 of the present invention;

[0048] Figure 12 It is a schematic diagram of another grid-connected current provided in Embodiment 2 of the present invention;

[0049] Figure 13 It is a schematic diagram of yet another grid-connected current provided in Embodiment 2 of the present invention;

[0050] Figure 14 It is a schematic diagram of yet another grid-connected current provided in Embodiment 2 of the present invention;

[0051] Figure 15 It is a structural block diagram of an impedance model determination device of a grid-connected inverter provided in Embodiment 3 of the present invention;

[0052] Figure 16 It is a schematic diagram of the structure of an electronic device provided in Embodiment 4 of the present invention. Detailed implementation manners

[0053] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only for explaining the present invention, rather than limiting the present invention. Additionally, it should be noted that for the sake of convenience of description, only parts related to the present invention rather than all structures are shown in the accompanying drawings.

[0054] Embodiment 1

[0055] Figure 1 It is a flowchart of a method for determining an impedance model of a grid-connected inverter provided in Embodiment 1 of the present invention. This embodiment is applicable to aspects such as determining the impedance model of a grid-connected inverter. This method can be executed by an impedance model determination device of a grid-connected inverter. This device can be integrated in an electronic device such as a computer. This device can be implemented in the form of software and / or hardware. The method specifically includes the following steps:

[0056] Step 110: Obtain the grid-connected parameters and grid-connected structure information of the grid-connected inverter.

[0057] Among them, the grid - connection parameters of the grid - connected inverter include grid - connection current and grid - connection voltage. Exemplarily, Figure 2 is a schematic diagram of grid - connection of a grid - connected inverter provided in the first embodiment of the present invention. Figure 2 The shown structural information is the grid - connection structure information. Refer to Figure 2 , U dc is the DC - side voltage of the grid - connected inverter, L1 and L2 are the output filter inductor of the grid - connected inverter and the filter inductor of the power grid respectively, R d is the filter resistor, C f is the filter capacitor, u o is the grid - connection voltage of the grid - connected inverter; the ideal grid voltage u g and the grid impedance Z g in series represent a weak grid, i o is the grid - connection current of the grid - connected inverter, I odref and I oqref respectively represent the components of the grid - connection current reference value on the d - axis and q - axis, G i(s) is the transfer function of the current controller, V Mα and V Mβ are the output modulation signals of two current controllers, PLL is a phase - locked loop, PCC is a grid - connection coupling point, K PWM is a constant, i oα and i oβ respectively represent the components of i o on the α - axis and β - axis, θ is the angle output by the PLL, abc / αβ represents the transformation from the abc three - phase coordinate axis to the αβ coordinate axis, dq / αβ represents the transformation from the dq coordinate axis to the αβ coordinate axis, and αβ / abc represents the transformation from the αβ coordinate axis to the abc three - phase coordinate axis. Figure 3 is a schematic diagram of the control structure of a grid - connected inverter provided in the first embodiment of the present invention. Refer to Figure 3 , the grid - connected inverter adopts the control structure as shown in Figure 3 for tracking and phase - locking. H PI (s)=k p-pll +k i-pll / s, u abc represents the abc three - phase voltage corresponding to u o , u d and u q are respectively the voltage of u abc transformed to the d - axis and the voltage of u abc transformed to the q - axis, ω o represents the actual output angular frequency of the PLL, ω ref is the grid reference angular frequency, H PI (s) represents the transfer function of the PI controller in the phase - locked loop, k p-pll represents the proportional coefficient of the PI controller in the phase - locked loop, k i-pllRepresents the integral coefficient of the PI controller in the phase-locked loop.

[0058] Step 120: Determine the basic mathematical model of the grid-connected inverter according to the grid-connection parameters.

[0059] Exemplarily, Figure 4 is a schematic diagram of the basic mathematical model of a grid-connected inverter provided in Embodiment 1 of the present invention. Refer to Figure 4 , i oαβref represents the reference value of i o on the αβ axis, and i odqref represents the reference value of i o on the dq axis. I o and U o respectively represent the output current and output voltage of the grid-connected inverter. G del (s) represents the delay transfer function; G1(s) and G2(s) are used to simplify the formula and have no practical meaning.

[0060] Step 130: Determine the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and the grid-connection parameters, and determine the continuous impedance model of the grid-connected inverter according to the small-signal impedance model.

[0061] Specifically, refer to Figure 4 , and the expression of I o in the s domain can be derived from the basic mathematical model of the grid-connected inverter where J(s) = G2(s)G1(s)K PWM G del (s)G i (s),

[0062]

[0063] Z L1 = sL1, Z L2 = sL2, Z Cf = R d + 1 / C f , and in combination with the PLL, the grid-connected voltage disturbance Δu o (s) and the transfer function between the grid-connected current disturbance Δi oref (s) can be obtained ω1 represents the grid fundamental angular frequency. Exemplarily, Figure 5 is a schematic diagram of the small-signal impedance model of a grid-connected inverter provided in Embodiment 1 of the present invention, Figure 6 is a schematic diagram of the equivalent small-signal circuit of a grid-connected inverter provided in Embodiment 1 of the present invention. Refer to Figure 5 , according to the above analysis, the following can be obtained as Figure 5The small-signal impedance model of the grid-connected inverter considering the PLL effect as shown can obtain the output current disturbance Δi of the grid-connected inverter after considering the PLL positive feedback loop according to the small-signal impedance model of Figure 5 The expression is oαβ where I is the amplitude of the rated grid-connected current. According to the above expression of the output current disturbance and the small-signal impedance model shown in m0 The equivalent small-signal circuit of the grid-connected inverter is as shown in Figure 5 Figure 6 The equivalent small-signal circuit is a Norton equivalent small-signal circuit. The inverter side is equivalent to two impedances Z(s), Z PLLαβ (s) in parallel, and the grid side is equivalent to an impedance. Among them, invαβ (s) Thus, the continuous impedance model of the grid-connected inverter is obtained

[0064] Step 140: Determine the hybrid small-signal model of the grid-connected inverter according to the basic mathematical model and grid-connected parameters and based on the discrete characteristics of the control system of the grid-connected inverter, and determine the hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model.

[0065] Specifically, according to the basic mathematical model and grid-connected parameters, based on the discrete characteristics of the control system of the grid-connected inverter, sample the continuous output voltage and output current of the grid-connected inverter to obtain the discretized output voltage and output current; establish a hybrid small-signal model according to the discretized output voltage and output current. According to the hybrid small-signal model, determine the equivalent hybrid small-signal circuit; the equivalent hybrid small-signal circuit is a circuit including the inverter side and the grid side; according to the equivalent hybrid small-signal circuit, determine the equivalent impedance of the grid-connected inverter to determine the hybrid impedance model.

[0066] Step 150: Determine the target impedance model according to the continuous impedance model and the hybrid impedance model.

[0067] Specifically, perform a stability analysis on the grid-connected inverter based on the hybrid impedance model and the continuous impedance model. If the grid-connected inverter operating based on the hybrid impedance model is unstable, and the grid-connected inverter operating based on the continuous impedance model is stable, and the actually operating grid-connected inverter is in an unstable state, then the analysis of the hybrid impedance model is correct, and the analysis of the continuous impedance model is incorrect. Determine the target impedance model as the hybrid impedance model.

[0068] The method for determining the impedance model of a grid-connected inverter provided in this embodiment determines the target impedance model according to the continuous impedance model and the hybrid impedance model. Specifically, based on the hybrid impedance model and the continuous impedance model, the stability of the grid-connected inverter is analyzed. If the grid-connected inverter is unstable based on the hybrid impedance model and stable based on the continuous impedance model, and the actually operating grid-connected inverter is in an unstable state, then the analysis of the hybrid impedance model is correct and the analysis of the continuous impedance model is incorrect. The target impedance model is determined to be the hybrid impedance model to ensure the accuracy of the impedance model and facilitate the stability analysis of the actual grid-connected system.

[0069] Embodiment 2

[0070] Figure 7 FIG. 3 is a flowchart of a method for determining the impedance model of a grid-connected inverter provided in Embodiment 2 of the present invention. This embodiment is applicable to aspects such as determining the impedance model of a grid-connected inverter. This method can be executed by a device for determining the impedance model of a grid-connected inverter, which can be integrated in an electronic device such as a computer, and the device can be implemented in the form of software and / or hardware. The method specifically includes the following steps:

[0071] Step 210: Obtain the grid connection parameters and grid connection structure information of the grid-connected inverter.

[0072] Step 220: Determine the basic mathematical model of the grid-connected inverter according to the grid connection parameters and grid connection structure information.

[0073] Among them, the grid connection parameters, grid connection structure information, and basic mathematical model can refer to Figures 2 - 4 and the description of Embodiment 1 above, which will not be elaborated here.

[0074] Step 230: Determine the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and the grid connection parameters, specifically including:

[0075] Determine the transfer function between the grid connection voltage disturbance and the grid connection current disturbance of the grid-connected inverter according to the basic mathematical model and the grid connection parameters;

[0076] Determine the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and the transfer function.

[0077] Step 240: Determine the continuous impedance model of the grid-connected inverter according to the small-signal impedance model, specifically including:

[0078] Determine the output current disturbance of the grid-connected inverter according to the small-signal impedance model;

[0079] Determine the equivalent small-signal circuit according to the small-signal impedance model and the output current disturbance; the equivalent small-signal circuit is a circuit including the inverter side and the grid side;

[0080] According to the equivalent small-signal circuit, determine the equivalent impedance of the grid-connected inverter to determine the continuous impedance model.

[0081] Among them, for the specific execution processes of steps 210 - 240, reference can be made to the specific description in Embodiment 1, which will not be elaborated here.

[0082] Step 250: Based on the basic mathematical model and grid-connected parameters, and considering the discrete characteristics of the control system of the grid-connected inverter, sample the continuous output voltage and output current of the grid-connected inverter to obtain the discretized output voltage and output current.

[0083] Exemplarily, Figure 8 is a schematic diagram of a hybrid structure of a grid-connected inverter provided in Embodiment 2 of the present invention. Refer to Figure 8 , the hybrid structure of the grid-connected inverter is a structure that simultaneously includes continuous and discrete time links (the construction process of the above continuous impedance model only includes continuous time links and does not consider the discrete characteristics of the control system of the grid-connected inverter, while the hybrid impedance model considers the discrete characteristics of the control system of the grid-connected inverter and the control system is discretized). Among them, the continuous output voltage U o and output current I o of the grid-connected inverter, after a sampling process with a sampling period of T s , the voltage and current are respectively obtained and controlled by a digital controller. On the premise of not considering the high-order harmonics caused by the switching process, the modulation signal obtained by the digital controller is converted into the actual output voltage of the grid-connected inverter via a ZOH (zero-order holder). Among them, "*" represents the sampling process, that is, the corresponding voltage, current, or controller transfer function is discretized.

[0084] Step 260: Based on the discretized output voltage and output current, establish a hybrid small-signal model of the grid-connected inverter.

[0085] Exemplarily, Figure 9 is a schematic diagram of a hybrid small-signal model of a grid-connected inverter provided in Embodiment 2 of the present invention. Refer to Figure 8 and Figure 9 , Figure 8 the hybrid structure shown can be represented by Figure 9 the hybrid small-signal model shown.

[0086] Step 270: According to the hybrid small-signal model, determine the hybrid impedance model of the grid-connected inverter, specifically including:

[0087] According to the hybrid small-signal model, determine the output voltage and output current of the hybrid small-signal model;

[0088] Determine an equivalent hybrid small-signal circuit based on the output voltage and output current of the hybrid small-signal model; the equivalent hybrid small-signal circuit is a circuit including an inverter side and a grid side;

[0089] Determine the equivalent impedance of the grid-connected inverter according to the equivalent hybrid small-signal circuit to determine the hybrid impedance model.

[0090] Specifically, Figure 9 The output voltage Δu o (s) and output current Δi o (s) of the shown hybrid small-signal model are obtained by sampling to get the sampled voltage and the sampled current G h (s) is the transfer function of the ZOH. Considering that the digital controller actually discretizes the signal, so for the current controller G Figure 9 (s) in it is discretized to obtain i (s), and the z operator is expressed as At the same time, the PLL performs the same processing to obtain the transfer function G (z), PLL wherein, From it can be obtained that Figure 9 Δi o =G2(s)[G1(s)G h (s)z -1 K PWM Δu m -Δu o , Δu m That is, m the Δu Figure 9 in o (s) represents the inverter output voltage after discretization processing in the rotating coordinate system, and Δi o That is, the above Δi m (s). According to the above expressions of Δu o and Δi h it can be deduced that wherein, F(s) = G2(s)G1(s)G -1 (s)z PWM K iαβ G o (z). Considering that the output current of the actual grid-connected inverter needs to be sampled by the digital controller, both sides of the above expression of Δi * are discretized to obtain That is, the above According to the discrete control theory and organizing the above expression, it is obtained that wherein, F* (s) = G2(z)G1(z)z -1 K PWM G iαβ (z). Since the impedance model of the grid-connected inverter should be the mathematical relationship between the continuous voltage Δu o and the continuous current Δi o between, so the expression of is substituted into Δi o the expression of can be obtained To obtain the correct mathematical relationship of the impedance model, for the above Δi containing F * (s), apply the Poisson theorem to the expression of, and express the discrete quantity in the formula o as the infinite series summation of continuous quantities, and finally organize to obtain the relationship between the continuous voltage and the continuous current To simplify the impedance model, ignore the infinite summation terms with n≠0 in the above formula and organize to obtain I m0 is the amplitude of the rated grid-connected current, U m0 is the amplitude of the rated grid-connected voltage, F*(s) = G2(z)G1(z)z -1 K PWM G iαβ (z), z is the operator, T s is the sampling period, K PWM is a constant. Exemplarily, Figure 10 is a schematic diagram of an equivalent hybrid small-signal circuit of a grid-connected inverter provided in the second embodiment of the present invention. The equivalent hybrid small-signal circuit is a Norton equivalent hybrid small-signal circuit. According to the above-organized expression of Δi o and Figure 9 the shown hybrid small-signal model, the Norton equivalent hybrid small-signal circuit as shown in Figure 10 can be obtained. The inverter side of the circuit is equivalent to two impedances in parallel, and the grid side is equivalent to one impedance. Among them, Thus, the hybrid impedance model of the grid-connected inverter is obtained Among them, is the equivalent impedance.

[0091] Step 280, perform stability analysis on the grid-connected inverter based on the hybrid impedance model and the continuous impedance model.

[0092] Exemplarily, Figure 11 is a schematic diagram of a grid-connected current provided in the second embodiment of the present invention. Figure 11 The waveform shown is L g= 10 mH, f PLL is the waveform of the grid-connected current when f g = 104 Hz, L PLL represents the grid inductance, f oa is the frequency bandwidth of the PLL, u o represents the phase-a voltage corresponding to u oabc includes i oa , i ob and i oc , i oa , i ob and i oc respectively represent the phase-a current, phase-b current, and phase-c current corresponding to i o . div represents the grid in the figure. After grid connection, the grid-connected inverter remains stable during both half-load and full-load operations. Figure 12 is another schematic diagram of the grid-connected current provided in Embodiment 2 of the present invention. Figure 12 The waveform shown is for L g = 11 mH, f PLL = 104 Hz of the grid-connected current waveform. After grid connection, the grid-connected inverter is in an oscillatory instability state during full-load operation. Figure 13 is yet another schematic diagram of the grid-connected current provided in Embodiment 2 of the present invention. Figure 13 The waveform shown is for L g = 12 mH, f PLL = 86 Hz of the grid-connected current waveform. After grid connection, the grid-connected inverter remains stable during both half-load and full-load operations. Figure 14 is yet another schematic diagram of the grid-connected current provided in Embodiment 2 of the present invention. Figure 14 The waveform shown is for L g = 12 mH, f PLL = 95 Hz of the grid-connected current waveform. After grid connection, the grid-connected inverter is in an oscillatory instability state during full-load operation. Among them, the parameters are shown in Table 1.

[0093] Table 1 Parameter Values

[0094]

[0095] Step 290: If the grid-connected inverter is operating unstably, and the grid-connected inverter based on the hybrid impedance model is operating unstably while the grid-connected inverter based on the continuous impedance model is operating stably, then determine the target impedance model as the hybrid impedance model.

[0096] Specifically, for Figure 11 and Figure 13 , the grid-connected inverter based on the hybrid impedance model is operating stably, and the grid-connected inverter based on the continuous impedance model is operating stably. The analysis of both models is correct. For Figure 12 and Figure 14, the grid-connected inverter operating based on the hybrid impedance model is unstable, while the grid-connected inverter operating based on the continuous impedance model is stable. There is an error in the analysis of the continuous impedance model, and the target impedance model is determined to be the hybrid impedance model.

[0097] The method for determining the impedance model of the grid-connected inverter provided in this embodiment determines the target impedance model according to the continuous impedance model and the hybrid impedance model, and conducts a stability analysis on the grid-connected inverter based on the hybrid impedance model and the continuous impedance model. If the grid-connected inverter operating based on the hybrid impedance model is unstable, the grid-connected inverter operating based on the continuous impedance model is stable, and the actually operating grid-connected inverter is in an unstable state, then the analysis of the hybrid impedance model is correct, the analysis of the continuous impedance model is incorrect, and the target impedance model is determined to be the hybrid impedance model to ensure the accuracy of the impedance model and facilitate the stability analysis of the actual grid-connected system.

[0098] Embodiment III

[0099] Figure 15 is the structural block diagram of an impedance model determination device for a grid-connected inverter provided in Embodiment III of the present invention. Refer to Figure 15 , the impedance model determination device for the grid-connected inverter includes: a parameter acquisition module 310, a basic model determination module 320, a continuous model determination module 330, a hybrid model determination module 340, and a target model determination module 350. Among them, the parameter acquisition module 310 is used to acquire the grid connection parameters and grid connection structure information of the grid-connected inverter; the basic model determination module 320 is used to determine the basic mathematical model of the grid-connected inverter according to the grid connection parameters and grid connection structure information; the continuous model determination module 330 is used to determine the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and the grid connection parameters, and determine the continuous impedance model of the grid-connected inverter according to the small-signal impedance model; the hybrid model determination module 340 is used to determine the hybrid small-signal model of the grid-connected inverter according to the basic mathematical model and the grid connection parameters and based on the discrete characteristics of the control system of the grid-connected inverter, and determine the hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model; the target model determination module 350 is used to determine the target impedance model according to the continuous impedance model and the hybrid impedance model.

[0100] Based on the above embodiment, the hybrid model determination module 340 includes:

[0101] a sampling unit, which is used to sample the continuous output voltage and output current of the grid-connected inverter according to the basic mathematical model and the grid connection parameters and based on the discrete characteristics of the control system of the grid-connected inverter to obtain the discretized output voltage and output current;

[0102] a model establishment unit, which is used to establish the hybrid small-signal model of the grid-connected inverter according to the discretized output voltage and output current.

[0103] In one embodiment, the hybrid model determination module 340 includes:

[0104] A circuit determination unit, configured to determine an equivalent hybrid small-signal circuit according to the hybrid small-signal model; the equivalent hybrid small-signal circuit is a circuit including an inverter side and a grid side;

[0105] A hybrid impedance model determination unit, configured to determine the equivalent impedance of the grid-connected inverter according to the equivalent hybrid small-signal circuit, so as to determine the hybrid impedance model.

[0106] Optionally, the above circuit determination unit includes:

[0107] A voltage and current determination subunit, configured to determine the output voltage and output current of the hybrid small-signal model according to the hybrid small-signal model;

[0108] A circuit determination subunit, configured to determine the equivalent hybrid small-signal circuit according to the output voltage and output current of the hybrid small-signal model.

[0109] Optionally, the target model determination module 350 includes:

[0110] A stability analysis unit, configured to perform stability analysis on the grid-connected inverter based on the hybrid impedance model and the continuous impedance model;

[0111] A target model determination unit, configured to, if the grid-connected inverter is unstable during operation and the grid-connected inverter is unstable based on the hybrid impedance model and stable based on the continuous impedance model, determine that the target impedance model is the hybrid impedance model.

[0112] Optionally, the continuous model determination module 330 includes:

[0113] A function determination unit, configured to determine the transfer function between the grid-connected voltage disturbance and the grid-connected current disturbance of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters;

[0114] A small-signal impedance model determination unit, configured to determine the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and the transfer function.

[0115] Optionally, the continuous model determination module 330 includes:

[0116] A current disturbance determination unit, configured to determine the output current disturbance of the grid-connected inverter according to the small-signal impedance model;

[0117] An equivalent small-signal circuit determination unit, configured to determine the equivalent small-signal circuit according to the small-signal impedance model and the output current disturbance; the equivalent small-signal circuit is a circuit including an inverter side and a grid side;

[0118] A continuous impedance model determination unit is configured to determine the equivalent impedance of a grid-connected inverter according to an equivalent small-signal circuit, so as to determine a continuous impedance model.

[0119] The impedance model determination device of the grid-connected inverter provided in this embodiment and the impedance model determination method of the grid-connected inverter provided in any embodiment of the present invention belong to the same inventive concept and have corresponding beneficial effects. For the technical details not elaborated in this embodiment, please refer to the impedance model determination method of the grid-connected inverter provided in any embodiment of the present invention.

[0120] Embodiment 4

[0121] Figure 16 It is a schematic structural diagram of an electronic device provided in Embodiment 4 of the present invention. Figure 16 It shows a block diagram of an exemplary electronic device 412 suitable for implementing the embodiments of the present invention. Figure 16 The shown electronic device 412 is only an example and should not impose any limitation on the functions and usage scope of the embodiments of the present invention.

[0122] As Figure 16 shown, the electronic device 412 is presented in the form of a general-purpose device. The components of the electronic device 412 may include, but are not limited to: one or more processors 416, a storage device 428, and a bus 418 connecting different system components (including the storage device 428 and the processor 416).

[0123] The bus 418 represents one or more of several types of bus structures, including a storage device bus or a storage device controller, a peripheral bus, a graphics acceleration port, a processor, or a local bus using any of the multiple bus structures. For example, these architectures include, but are not limited to, the Industry Subversive Alliance (ISA) bus, the Micro Channel Architecture (MAC) bus, the Enhanced ISA bus, the Video Electronics Standards Association (VESA) local bus, and the Peripheral Component Interconnect (PCI) bus.

[0124] The electronic device 412 typically includes a variety of computer system-readable media. These media can be any available media accessible by the electronic device 412, including volatile and non-volatile media, removable and non-removable media.

[0125] The storage device 428 may include computer system readable media in the form of volatile memory, such as random access memory (RAM) 430 and / or cache memory 432. The electronic device 412 may further include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, the storage system 434 may be used for reading and writing on non-removable, non-volatile magnetic media ( Figure 16 not shown, commonly referred to as a "hard disk drive"). Although Figure 16 not shown in, a disk drive for reading and writing on removable non-volatile disks (such as a "floppy disk"), and an optical disk drive for reading and writing on removable non-volatile optical disks, such as a compact disc read-only memory (CD-ROM), a digital video disc read-only memory (DVD-ROM) or other optical media) may be provided. In these cases, each drive may be connected to the bus 418 through one or more data media interfaces. The storage device 428 may include at least one program product having a set (e.g., at least one) of program modules configured to perform the functions of the embodiments of the present invention.

[0126] A program / utility 440 having a set (at least one) of program modules 442 may be stored, for example, in the storage device 428. Such program modules 442 include, but are not limited to, an operating system, one or more application programs, other program modules, and program data. Each or some combination of these examples may include the implementation of a network environment. The program modules 442 generally perform the functions and / or methods in the embodiments described in the present invention.

[0127] The electronic device 412 may also communicate with one or more external devices 414 (such as a keyboard, a pointing terminal, a display 424, etc.), and may also communicate with one or more terminals that enable a user to interact with the electronic device 412, and / or communicate with any terminal that enables the electronic device 412 to communicate with one or more other computing terminals (such as a network card, a modem, etc.). Such communication may be carried out through the input / output (I / O) interface 422. Further, the electronic device 412 may also communicate with one or more networks (such as a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) through the network adapter 420. As Figure 16As shown, network adapter 420 communicates with other modules of electronic device 412 via bus 418. It should be understood that, although not shown in the figure, other hardware and / or software modules may be used in conjunction with electronic device 412, including but not limited to: microcode, terminal drivers, redundant processors, external disk drive arrays, redundant arrays of independent disks (RAID) systems, tape drives, and data backup storage systems, etc.

[0128] Processor 416 executes various functional applications and data processing by running programs stored in storage device 428, such as implementing the method for determining the impedance model of a grid-connected inverter provided in an embodiment of the present invention. The method includes:

[0129] Obtain the grid-connected parameters and grid-connected structure information of the grid-connected inverter;

[0130] Determine the basic mathematical model of the grid-connected inverter according to the grid-connected parameters and grid-connected structure information;

[0131] Determine the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and grid-connected parameters, and determine the continuous impedance model of the grid-connected inverter according to the small-signal impedance model;

[0132] Determine the hybrid small-signal model of the grid-connected inverter according to the grid-connected parameters and grid-connected structure information, and based on the discrete characteristics of the control system of the grid-connected inverter, and determine the hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model;

[0133] Determine the target impedance model according to the continuous impedance model and the hybrid impedance model.

[0134] Embodiment Five

[0135] Embodiment Five of the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, it implements the method for determining the impedance model of a grid-connected inverter provided in an embodiment of the present invention. The method includes:

[0136] Obtain the grid-connected parameters and grid-connected structure information of the grid-connected inverter;

[0137] Determine the basic mathematical model of the grid-connected inverter according to the grid-connected parameters and grid-connected structure information;

[0138] Determine the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and grid-connected parameters, and based on the discrete characteristics of the control system of the grid-connected inverter, and determine the continuous impedance model of the grid-connected inverter according to the small-signal impedance model;

[0139] Determine the hybrid small-signal model of the grid-connected inverter according to the grid-connection parameters and grid-connection structure information and based on the discrete characteristics, and determine the hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model;

[0140] Determine the target impedance model according to the continuous impedance model and the hybrid impedance model.

[0141] The computer storage medium of the embodiments of the present invention may adopt any combination of one or more computer-readable media. The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The computer-readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination of the above. More specific examples (non-exhaustive list) of the computer-readable storage medium include: an electrical connection having one or more wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this document, the computer-readable storage medium may be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0142] The computer-readable signal medium may include a data signal propagated in a baseband or as part of a carrier wave, which carries the computer-readable program code. Such a propagated data signal may take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. The computer-readable signal medium may also be any computer-readable medium other than the computer-readable storage medium, which can send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, apparatus, or device.

[0143] The program code contained on the computer-readable medium can be transmitted by any suitable medium, including but not limited to wireless, wire, optical cable, RF, etc., or any suitable combination of the above.

[0144] Computer program code for performing the operations of the present invention may be written in one or more programming languages or combinations thereof, including object-oriented programming languages such as Java, Smalltalk, C++, and also including conventional procedural programming languages such as the "C" language or similar programming languages. The program code may execute entirely on the user's computer, partially on the user's computer, execute as a stand-alone software package, execute partially on the user's computer and partially on a remote computer, or execute entirely on a remote computer or terminal. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., through the Internet using an Internet service provider).

[0145] Note that the above is only the preferred embodiment of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, re-modulations, combinations, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, more other equivalent embodiments may be included, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for determining the impedance model of a grid-connected inverter, characterized in that, Including: Obtaining grid - connection parameters and grid - connection structure information of a grid - connected inverter; Determining a basic mathematical model of the grid - connected inverter according to the grid - connection parameters and the grid - connection structure information; Determining a small - signal impedance model of the grid - connected inverter according to the basic mathematical model and the grid - connection parameters, and determining a continuous impedance model of the grid - connected inverter according to the small - signal impedance model; Determining a hybrid small - signal model of the grid - connected inverter according to the basic mathematical model and the grid - connection parameters and based on the discrete characteristics of the control system of the grid - connected inverter, and determining a hybrid impedance model of the grid - connected inverter according to the hybrid small - signal model; Determining a target impedance model according to the continuous impedance model and the hybrid impedance model.

2. The method for determining the impedance model of the grid-connected inverter according to claim 1, characterized in that, The step of determining the hybrid small - signal model according to the basic mathematical model and the grid - connection parameters and based on the discrete characteristics of the control system of the grid - connected inverter includes: Sampling the continuous output voltage and output current of the grid - connected inverter according to the basic mathematical model and the grid - connection parameters and based on the discrete characteristics of the controller system of the grid - connected inverter to obtain the discretized output voltage and output current; Establishing the hybrid small - signal model according to the discretized output voltage and output current.

3. The method for determining the impedance model of the grid-connected inverter according to claim 1, characterized in that, The step of determining the hybrid impedance model of the grid - connected inverter according to the hybrid small - signal model includes: Determining an equivalent hybrid small - signal circuit according to the hybrid small - signal model; the equivalent hybrid small - signal circuit is a circuit including an inverter side and a grid side; Determining the equivalent impedance of the grid - connected inverter according to the equivalent hybrid small - signal circuit to determine the hybrid impedance model.

4. The method for determining the impedance model of the grid-connected inverter according to claim 3, wherein The step of determining the equivalent hybrid small - signal circuit according to the hybrid small - signal model includes: Determining the output voltage and output current of the hybrid small - signal model according to the hybrid small - signal model; Determining the equivalent hybrid small - signal circuit according to the output voltage and output current of the hybrid small - signal model.

5. The method for determining the impedance model of the grid-connected inverter according to claim 3, wherein The described hybrid impedance model Wherein is the equivalent impedance and are respectively two parallel impedances on the inverter side in the equivalent hybrid small-signal circuit 6. The method for determining the impedance model of the grid-connected inverter according to claim 1, characterized in that The step of determining the target impedance model according to the continuous impedance model and the hybrid impedance model includes: Performing a stability analysis on the grid - connected inverter based on the hybrid impedance model and the continuous impedance model; If the grid - connected inverter is unstable during operation, and the grid - connected inverter is unstable based on the hybrid impedance model and stable based on the continuous impedance model, then determining the target impedance model as the hybrid impedance model.

7. The method for determining the impedance model of the grid-connected inverter according to claim 1, characterized in that The step of determining the small - signal impedance model of the grid - connected inverter according to the basic mathematical model and the grid - connection parameters includes: Determining the transfer function between the grid - connection voltage disturbance and the grid - connection current disturbance of the grid - connected inverter according to the basic mathematical model and the grid - connection parameters; Determining the small - signal impedance model of the grid - connected inverter according to the basic mathematical model and the transfer function.

8. The method for determining the impedance model of the grid-connected inverter according to claim 7, wherein The step of determining the continuous impedance model of the grid - connected inverter according to the small - signal impedance model includes: Determining the output current disturbance of the grid - connected inverter according to the small - signal impedance model; Determine an equivalent small-signal circuit according to the small-signal impedance model and the output current perturbation; the equivalent small-signal circuit is a circuit including an inverter side and a grid side; Determine the equivalent impedance of the grid-connected inverter according to the equivalent small-signal circuit to determine the continuous impedance model.

9. The method for determining the impedance model of the grid-connected inverter according to claim 1, wherein There is a functional relationship between the output voltage and the output current of the hybrid small-signal model.

10. An impedance model determination device for a grid-connected inverter, characterized in that, It includes: A parameter acquisition module for acquiring grid-connected parameters and grid-connected structure information of the grid-connected inverter; A basic model determination module for determining the basic mathematical model of the grid-connected inverter according to the grid-connected parameters and the grid-connected structure information; A continuous model determination module for determining the small-signal impedance model of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters, and determining the continuous impedance model of the grid-connected inverter according to the small-signal impedance model; A hybrid model determination module for determining the hybrid small-signal model of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters and based on the discrete characteristics of the control system of the grid-connected inverter, and determining the hybrid impedance model of the grid-connected inverter according to the hybrid small-signal model; A target model determination module for determining the target impedance model according to the continuous impedance model and the hybrid impedance model.

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