A method and apparatus for determining the impedance model of a grid-connected inverter

Abstract

This invention discloses a method and apparatus for determining the hybrid impedance model of a grid-connected inverter. The method includes: determining a basic mathematical model and a hybrid small-signal model of the grid-connected inverter based on grid-connected parameters and grid structure information; determining a small-signal impedance model of the grid-connected inverter based on the basic mathematical model and grid-connected parameters, and determining a continuous impedance model of the grid-connected inverter based on the small-signal impedance model; determining a hybrid small-signal model of the grid-connected inverter based on the basic mathematical model and grid-connected parameters, and based on the discrete characteristics of the grid-connected inverter's control system, and determining a hybrid impedance model of the grid-connected inverter based on the hybrid small-signal model; and determining a target impedance model based on the continuous impedance model and the hybrid impedance model. The technical solution provided by this invention ensures the accuracy of the impedance model and facilitates stability analysis of actual grid-connected systems.

Description

Technical Field

[0001] The embodiments of the present invention relate to inverter grid connection technology, and more particularly to a method and apparatus for determining the impedance model of a grid-connected inverter. Background Technology

[0002] The presence of high grid impedance in weak grid environments, coupled with the negative impact of phase-locked loops (PLLs), can cause resonance phenomena in inverters during grid connection. To analyze the stability of grid-connected inverters, it is necessary to determine their impedance model. However, traditional methods for determining the impedance model of grid-connected inverters suffer from poor accuracy when analyzing the oscillating instability state of grid-connected inverters under weak grid conditions. Summary of the Invention

[0003] This invention provides a method and apparatus for determining the impedance model of a grid-connected inverter, so as to ensure the accuracy of the impedance model and facilitate stability analysis of actual grid-connected systems.

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

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

[0006] Based on the grid connection parameters and grid connection structure information, the basic mathematical model of the grid-connected inverter is determined;

[0007] Based on the basic mathematical model and the grid connection parameters, and based on the discrete characteristics of the control system of the grid-connected inverter, the hybrid small-signal model of the grid-connected inverter is determined, and based on the hybrid small-signal model, the hybrid impedance model of the grid-connected inverter is determined.

[0008] The target impedance model is determined based on the continuous impedance model and the hybrid impedance model.

[0009] Optionally, determining the hybrid small-signal model based on 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] Based on the basic mathematical model and the grid connection parameters, and based on the discrete characteristics of the control system of the grid-connected inverter, the continuous output voltage and output current of the grid-connected inverter are sampled to obtain the discrete output voltage and output current.

[0011] Based on the discretized output voltage and output current, the hybrid small-signal model is established.

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

[0013] Based on the hybrid small-signal model, an equivalent hybrid small-signal circuit is determined; the equivalent hybrid small-signal circuit includes circuits on both the inverter side and the grid side.

[0014] Based on the equivalent hybrid small-signal circuit, the equivalent impedance of the grid-connected inverter is determined, thereby determining the hybrid impedance model.

[0015] Optionally, determining the equivalent mixed small-signal circuit based on the mixed small-signal model includes:

[0016] Based on the hybrid small-signal model, determine the output voltage and output current of the hybrid small-signal model;

[0017] Based on 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 in, The equivalent impedance is... and These are the two parallel impedances on the inverter side of the equivalent hybrid small-signal circuit.

[0019] Optionally, determining the target impedance model based on the continuous impedance model and the hybrid impedance model includes:

[0020] Stability analysis of the grid-connected inverter is performed based on the hybrid impedance model and the continuous impedance model.

[0021] If the grid-connected inverter operates unstable when the operation is based on the hybrid impedance model, but the grid-connected inverter operates stably when the operation is based on the continuous impedance model, then the target impedance model is determined to be the hybrid impedance model.

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

[0023] Based on 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] Based on the basic mathematical model and the transfer function, the small-signal impedance model of the grid-connected inverter is determined.

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

[0026] The output current disturbance of the grid-connected inverter is determined based on the small-signal impedance model.

[0027] Based on the small-signal impedance model and the output current disturbance, the equivalent small-signal circuit is determined; the equivalent small-signal circuit includes circuits on both the inverter side and the grid side.

[0028] Based on the equivalent small-signal circuit, the equivalent impedance of the grid-connected inverter is determined, thereby determining the continuous impedance model.

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

[0030] Secondly, embodiments of the present invention provide an impedance model determination device for a grid-connected inverter, comprising:

[0031] The parameter acquisition module is used to acquire the grid connection parameters and grid connection structure information of the grid-connected inverter;

[0032] The basic model determination module is used to determine the basic mathematical model of the grid-connected inverter based on the grid connection parameters and grid connection structure information;

[0033] The continuous model determination module is used to determine the small-signal impedance model of the grid-connected inverter based on the basic mathematical model and the grid-connected parameters, and to determine the continuous impedance model of the grid-connected inverter based on the small-signal impedance model.

[0034] The hybrid model determination module is used to determine the hybrid small-signal model of the grid-connected inverter based on the basic mathematical model and the grid-connected parameters and the discrete characteristics of the control system of the grid-connected inverter, and to determine the hybrid impedance model of the grid-connected inverter based on the hybrid small-signal model;

[0035] The target model determination module is used to determine the target impedance model based on the continuous impedance model and the hybrid impedance model.

[0036] The present invention provides a method and apparatus for determining the impedance model of a grid-connected inverter. The method for determining the impedance model of a grid-connected inverter includes: acquiring grid-connected parameters and grid-connected structure information of the grid-connected inverter; determining the basic mathematical model of the grid-connected inverter based on the grid-connected parameters and grid-connected structure information; determining the small-signal impedance model of the grid-connected inverter based on the basic mathematical model and grid-connected parameters, and determining the continuous impedance model of the grid-connected inverter based on the small-signal impedance model; determining the hybrid small-signal model of the grid-connected inverter based on the basic mathematical model and 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 based on the hybrid small-signal model; and determining the target impedance model based on the continuous impedance model and the hybrid impedance model. The impedance model determination method and apparatus for grid-connected inverters provided in this invention determine the target impedance model based on a continuous impedance model and a hybrid impedance model. Specifically, stability analysis of the grid-connected inverter is performed based on the hybrid impedance model and the continuous impedance model. If the grid-connected inverter obtained based on the hybrid impedance model is unstable, while the grid-connected inverter obtained based on the continuous impedance model is stable, and the actual 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 then determined to be the hybrid impedance model to ensure the accuracy of the impedance model and facilitate stability analysis of the actual grid-connected system. Attached Figure Description

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

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

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

[0040] Figure 4 This 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 This is a schematic diagram of a small-signal impedance model of a grid-connected inverter provided in Embodiment 1 of the present invention;

[0042] Figure 6 This 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 This is a flowchart of a method for determining the impedance model of a grid-connected inverter according to Embodiment 2 of the present invention;

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

[0045] Figure 9 This 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 This is a schematic diagram of an equivalent hybrid small-signal circuit for a grid-connected inverter provided in Embodiment 2 of the present invention;

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

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

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

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

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

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

[0053] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0054] Example 1

[0055] Figure 1 This is a flowchart of a method for determining the impedance model of a grid-connected inverter according to Embodiment 1 of the present invention. This embodiment can be applied to determining the impedance model of a grid-connected inverter, etc. This method can be executed by an impedance model determination device for a grid-connected inverter. This device can be integrated into 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 connection parameters and grid connection structure information of the grid-connected inverter.

[0057] The grid-connected parameters of the grid-connected inverter include grid-connected current and grid-connected voltage. For example, Figure 2 This is a schematic diagram of a grid-connected inverter provided in Embodiment 1 of the present invention. Figure 2 The structural information shown is the grid connection structure information, for reference. Figure 2 U dc R is the DC-side voltage of the grid-connected inverter, L1 and L2 are the output filter inductance of the grid-connected inverter and the filter inductance of the grid, respectively. d For the filter resistor, C f For the filter capacitor, u o The grid connection voltage of the grid-connected inverter; the ideal grid voltage u. g and grid impedance Z g Series connection represents a weak power grid, i o I is the grid-connected current of the grid-connected inverter. odref and I oqref G represents the components of the grid-connected current reference value on the d-axis and q-axis, respectively. i(s) V is the transfer function of the current controller. Mα and V Mβ The output modulation signals of the two current controllers are: PLL (phase-locked loop) and PCC (grid coupling point). K PWM i is a constant. oα and i oβ Representing i respectively o In the components of the α and β axes, 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 This is a schematic diagram of the control structure of a grid-connected inverter provided in Embodiment 1 of the present invention. (Reference) Figure 3 Grid-connected inverters adopt such as Figure 3 The control structure shown performs tracking phase-locked loop, H PI (s)=k p-pll +k i-pll / s,u abc Indicate u o The corresponding three-phase voltages abc, u d and u q u abc Voltage transformed to the d-axis and u abc Voltage transformed to the q-axis, ω o ω represents the actual output angular frequency of the PLL. ref H is the reference angular frequency of the power grid. PI (s) represents the transfer function of the PI controller in the phase-locked loop, k p-pll k represents the proportional gain of the PI controller in the phase-locked loop. i-pllThis represents 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 based on the grid connection parameters.

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

[0060] Step 130: Based on the basic mathematical model and grid connection parameters, determine the small-signal impedance model of the grid-connected inverter, and then determine the continuous impedance model of the grid-connected inverter based on the small-signal impedance model.

[0061] For details, please refer to Figure 4 Based on the basic mathematical model of the grid-connected inverter, I can be derived. o Expressions in the s domain 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 By combining the PLL, the grid-connected voltage disturbance Δu of the grid-connected inverter can be obtained. o (s) and grid-connected current disturbance Δi oref Transfer function between (s) ω1 represents the fundamental angular frequency of the power grid. For example, Figure 5 This is a schematic diagram of a small-signal impedance model of a grid-connected inverter provided in Embodiment 1 of the present invention. Figure 6 This is a schematic diagram of the equivalent small-signal circuit of a grid-connected inverter provided in Embodiment 1 of the present invention. (Reference) Figure 5 Based on the above analysis, we can obtain the following: Figure 5The small-signal impedance model of the grid-connected inverter considering the influence of the PLL is shown below, based on... Figure 5 The small-signal impedance model can be used to calculate the output current disturbance Δi of the grid-connected inverter after considering the PLL positive feedback loop. oαβ The expression is Among them, I m0 This is the amplitude of the rated grid-connected current. Based on the above expression for output current disturbance and... Figure 5 The small-signal impedance model shown is illustrated, and the equivalent small-signal circuit of the grid-connected inverter is as follows: Figure 6 As shown, the equivalent small-signal circuit is the Norton equivalent small-signal circuit, and the inverter side is equivalent to two impedances Z. PLLαβ (s), Z invαβ (s) In parallel connection, the grid side is equivalent to a single impedance. Wherein, Thus, the continuous impedance model of the grid-connected inverter is obtained.

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

[0065] Specifically, based on the basic mathematical model and grid-connected parameters, and taking into account the discrete characteristics of the grid-connected inverter's control system, the continuous output voltage and current of the grid-connected inverter are sampled to obtain discretized output voltage and current. Based on the discretized output voltage and current, a hybrid small-signal model is established. According to the hybrid small-signal model, an equivalent hybrid small-signal circuit is determined; this equivalent hybrid small-signal circuit includes circuits from both the inverter side and the grid side. Based on the equivalent hybrid small-signal circuit, the equivalent impedance of the grid-connected inverter is determined, thus establishing the hybrid impedance model.

[0066] Step 150: Determine the target impedance model based on the continuous impedance model and the mixed impedance model.

[0067] Specifically, stability analysis of grid-connected inverters is performed based on hybrid impedance models and continuous impedance models. If the grid-connected inverter based on the hybrid impedance model is unstable, while the grid-connected inverter based on the continuous impedance model is stable, and the actual 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.

[0068] The impedance model determination method for grid-connected inverters provided in this embodiment determines the target impedance model based on a continuous impedance model and a hybrid impedance model. Specifically, stability analysis of the grid-connected inverter is performed based on the hybrid impedance model and the continuous impedance model. If the grid-connected inverter based on the hybrid impedance model is unstable, while the grid-connected inverter based on the continuous impedance model is stable, and the actual 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 then determined to be the hybrid impedance model to ensure the accuracy of the impedance model and facilitate stability analysis of the actual grid-connected system.

[0069] Example 2

[0070] Figure 7 This is a flowchart of a method for determining the impedance model of a grid-connected inverter according to Embodiment 2 of the present invention. This embodiment can be applied to determining the impedance model of a grid-connected inverter, etc. This method can be executed by an impedance model determination device for a grid-connected inverter. This device can be integrated into 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:

[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 based on the grid connection parameters and grid structure information.

[0073] Among them, grid connection parameters, grid structure information, and basic mathematical models can be referenced. Figures 2-4 The description of Embodiment 1 above will not be repeated here.

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

[0075] Based on the basic mathematical model and 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.

[0076] Based on the basic mathematical model and transfer function, the small-signal impedance model of the grid-connected inverter is determined.

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

[0078] The output current disturbance of the grid-connected inverter is determined based on the small-signal impedance model.

[0079] Based on the small-signal impedance model and output current disturbance, the equivalent small-signal circuit is determined; the equivalent small-signal circuit includes the inverter side and the grid side.

[0080] Based on the equivalent small-signal circuit, the equivalent impedance of the grid-connected inverter is determined, thereby establishing the continuous impedance model.

[0081] The specific execution process of steps 210-240 can be referred to the detailed description in Embodiment 1, and will not be repeated here.

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

[0083] For example, Figure 8 This is a schematic diagram of a hybrid structure of a grid-connected inverter provided in Embodiment 2 of the present invention. (Reference) Figure 8 The hybrid structure of the grid-connected inverter includes both continuous and discrete-time components (the continuous impedance model described above only includes the continuous-time component and does not consider the discrete characteristics of the grid-connected inverter's control system; the hybrid impedance model considers the discrete characteristics of the grid-connected inverter's control system and discretizes the control system). The continuous output voltage U of the grid-connected inverter... o and output current I o After a sampling period of T s After the sampling process, voltage and current are obtained respectively. It is controlled by a digital controller. Ignoring 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). Here, "*" indicates the sampling process, i.e., the discretization of the corresponding voltage, current, or controller transfer function.

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

[0085] For example, Figure 9 This is a schematic diagram of a hybrid small-signal model of a grid-connected inverter provided in Embodiment 2 of the present invention. (Reference) Figure 8 and Figure 9 , Figure 8 The hybrid structure shown can be derived from Figure 9 The mixed small-signal model shown is illustrated.

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

[0087] Based on the mixed small-signal model, determine the output voltage and output current of the mixed small-signal model;

[0088] Based on the output voltage and output current of the hybrid small-signal model, the equivalent hybrid small-signal circuit is determined; the equivalent hybrid small-signal circuit includes both the inverter side and the grid side.

[0089] Based on the equivalent hybrid small-signal circuit, the equivalent impedance of the grid-connected inverter is determined, thereby establishing the hybrid impedance model.

[0090] Specifically, Figure 9 The output voltage Δu of the mixed small-signal model shown o (s) and output current Δi o (s), the sampling voltage is obtained through sampling. and sampling current G h (s) is the transfer function of ZOH. Considering that digital controllers actually discretize signals, therefore... Figure 9 Medium current controller G i (s) discretization yields The z operator is represented as Simultaneously, the PLL performs the same processing to obtain the transfer function G. PLL (z), in, Depend on Figure 9 achievable Δi o =G2(s)[G1(s)G h (s)z -1 K PWM Δu m -Δu o ],Δu m Right now Figure 9 Δu m (s) represents the inverter output voltage after discretization in the rotating coordinate system, Δi o That is, the above Δi o (s), according to the above Δu m and Δi o The expression can be derived Where F(s)=G2(s)G1(s)G h (s)z -1 K PWM G iαβ (z). Considering that the output current of the actual grid-connected inverter needs to be sampled by the digital controller, the above Δi o Discretizing both sides of the expression simultaneously yields That is, the above Based on discrete control theory and summarizing the above... The expression is obtained Among them, F* (s)=G2(z)G1(z)z -1 K PWM G iαβ (z). Since the impedance model of the grid-connected inverter should be a continuous voltage Δu o and continuous current Δi o The mathematical relationship between them, therefore Substituting the expression into Δi o The expression can be obtained To obtain the correct mathematical relationship for the impedance model, the above-mentioned components containing F... * Δi of (s) o Applying Poisson's theorem to the expression, the discrete quantities in the formula are... This can be expressed as the sum of an infinite series of continuous quantities, which, when rearranged, yields the relationship between continuous voltage and continuous current. To simplify the impedance model, we ignore the infinite summation terms where n≠0 in the above formula and rearrange to obtain the following result. I m0 The amplitude of the rated grid-connected current. U m0 The amplitude of the rated grid-connected voltage is F*(s) = G2(z)G1(z)z -1 K PWM G iαβ (z), where z is the operator. T s K is the sampling period. PWM It is a constant. For example, Figure 10 This is a schematic diagram of the equivalent mixed-signal circuit of a grid-connected inverter provided in Embodiment 2 of the present invention. The equivalent mixed-signal circuit is the Norton equivalent mixed-signal circuit, and the Δi obtained above is... o expressions and Figure 9 The mixed small-signal model shown can yield the following results: Figure 10 The Norton equivalent mixed-signal circuit shown has two equivalent impedances on the inverter side. In parallel connection, the grid side is equivalent to a single impedance. Among them, Thus, the hybrid impedance model of the grid-connected inverter is obtained. in, This 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] For example, Figure 11 This is a schematic diagram of a grid-connected current provided in Embodiment 2 of the present invention. Figure 11 The waveform shown is L g=10mH, f PLL The waveform of the grid-connected current at 104Hz, L g f represents the mains inductance. PLL u is the frequency bandwidth of the PLL. oa Indicate u o The corresponding phase a voltage, i oabc Including i oa i ob and i oc i oa i ob and i oc Representing i respectively o The corresponding phase a current, phase b current, and phase c current are shown in the diagram. div represents the grid cells in the diagram. The grid-connected inverter remains stable under both half-load and full-load operation after grid connection. Figure 12 This is a schematic diagram of another grid-connected current provided in Embodiment 2 of the present invention. Figure 12 The waveform shown is L g =11mH, f PLL The waveform of the grid-connected current at 104Hz indicates that the grid-connected inverter is in an oscillating and unstable state when operating at full load after grid connection. Figure 13 This is a schematic diagram of another grid-connected current provided in Embodiment 2 of the present invention. Figure 13 The waveform shown is L g =12mH, f PLL The waveform of the grid-connected current at 86Hz shows that the grid-connected inverter remains stable under both half-load and full-load operation after grid connection. Figure 14 This is a schematic diagram of another grid-connected current provided in Embodiment 2 of the present invention. Figure 14 The waveform shown is L g =12mH, f PLL The waveform of the grid-connected current at 95Hz is shown in Table 1. After grid connection, the grid-connected inverter is in an oscillating and unstable state under full load operation. The parameters are shown in Table 1.

[0093] Table 1 Parameter Values

[0094]

[0095] Step 290: If the grid-connected inverter operates unstablely, and the grid-connected inverter obtained based on the hybrid impedance model operates unstablely, while the grid-connected inverter obtained based on the continuous impedance model operates stably, then the target impedance model is determined to be the hybrid impedance model.

[0096] Specifically, for Figure 11 and Figure 13 The grid-connected inverter based on the hybrid impedance model operates stably, as does the grid-connected inverter based on the continuous impedance model. The analyses of both models are correct. Figure 12 and Figure 14The grid-connected inverter based on the hybrid impedance model is unstable, while the grid-connected inverter based on the continuous impedance model is stable. The analysis of the continuous impedance model is incorrect, and the target impedance model is determined to be the hybrid impedance model.

[0097] The impedance model determination method for grid-connected inverters provided in this embodiment determines the target impedance model based on a continuous impedance model and a hybrid impedance model. Stability analysis of the grid-connected inverter is then performed based on both the hybrid and continuous impedance models. If the grid-connected inverter based on the hybrid impedance model is unstable, while the one based on the continuous impedance model is stable, and the actual operating grid-connected inverter is in an unstable state, then the analysis using the hybrid impedance model is correct, and the analysis using the continuous impedance model is incorrect. Therefore, the target impedance model is determined to be the hybrid impedance model to ensure the accuracy of the impedance model and facilitate stability analysis of the actual grid-connected system.

[0098] Example 3

[0099] Figure 15 This is a structural block diagram of an impedance model determination device for a grid-connected inverter provided in Embodiment 3 of the present invention. (Reference) Figure 15 The impedance model determination device for a 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. Specifically, the parameter acquisition module 310 acquires the grid-connected parameters and grid structure information of the grid-connected inverter; the basic model determination module 320 determines the basic mathematical model of the grid-connected inverter based on the grid-connected parameters and grid structure information; the continuous model determination module 330 determines the small-signal impedance model of the grid-connected inverter based on the basic mathematical model and grid-connected parameters, and determines the continuous impedance model of the grid-connected inverter based on the small-signal impedance model; the hybrid model determination module 340 determines the hybrid small-signal model of the grid-connected inverter based on the basic mathematical model, grid-connected parameters, and the discrete characteristics of the control system of the grid-connected inverter, and determines the hybrid impedance model of the grid-connected inverter based on the hybrid small-signal model; and the target model determination module 350 determines the target impedance model based on the continuous impedance model and the hybrid impedance model.

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

[0101] The sampling unit is used to sample the continuous output voltage and output current of the grid-connected inverter based on the basic mathematical model and 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.

[0102] The model building unit is used to build a hybrid small-signal model of the grid-connected inverter based on the discretized output voltage and output current.

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

[0104] The circuit determination unit is used to determine the equivalent mixed small-signal circuit based on the mixed small-signal model; the equivalent mixed small-signal circuit includes circuits on both the inverter side and the grid side.

[0105] The hybrid impedance model determination unit is used to determine the equivalent impedance of the grid-connected inverter based on the equivalent hybrid small-signal circuit, so as to determine the hybrid impedance model.

[0106] Optionally, the circuit determining unit mentioned above includes:

[0107] The voltage and current determination subunit is used to determine the output voltage and output current of the mixed small-signal model based on the mixed small-signal model.

[0108] The circuit determination sub-unit is used to determine the equivalent mixed small-signal circuit based on the output voltage and output current of the mixed small-signal model.

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

[0110] The stability analysis unit is used to perform stability analysis on grid-connected inverters based on hybrid impedance models and continuous impedance models.

[0111] The target model determination unit is used to determine the target impedance model as the hybrid impedance model if the grid-connected inverter operates unstable when the grid-connected inverter is based on the hybrid impedance model, but the grid-connected inverter operates stably when the grid-connected inverter is based on the continuous impedance model.

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

[0113] The function determination unit is used to determine the transfer function between the grid-connected voltage disturbance and the grid-connected current disturbance of the grid-connected inverter based on the basic mathematical model and grid-connected parameters.

[0114] The small-signal impedance model determination unit is used to determine the small-signal impedance model of the grid-connected inverter based on the basic mathematical model and transfer function.

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

[0116] The current disturbance determination unit is used to determine the output current disturbance of the grid-connected inverter based on the small-signal impedance model.

[0117] The equivalent small-signal circuit determination unit is used to determine the equivalent small-signal circuit based on the small-signal impedance model and output current disturbance; the equivalent small-signal circuit includes circuits on both the inverter side and the grid side.

[0118] The continuous impedance model determination unit is used to determine the equivalent impedance of the grid-connected inverter based on the equivalent small-signal circuit, so as to determine the continuous impedance model.

[0119] The impedance model determination device for grid-connected inverters provided in this embodiment belongs to the same inventive concept as the impedance model determination method for grid-connected inverters provided in any embodiment of the present invention, and has corresponding beneficial effects. For technical details not detailed in this embodiment, please refer to the impedance model determination method for grid-connected inverters provided in any embodiment of the present invention.

[0120] Example 4

[0121] Figure 16 This is a schematic diagram of the structure of an electronic device provided in Embodiment 4 of the present invention. Figure 16 A block diagram is shown of an exemplary electronic device 412 suitable for implementing embodiments of the present invention. Figure 16 The electronic device 412 shown is merely an example and should not impose any limitation on the functionality and scope of use of the embodiments of the present invention.

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

[0123] Bus 418 represents one or more of several bus architectures, including a memory device bus or memory device controller, a peripheral bus, a graphics acceleration port, a processor, or a local bus using any of the various bus architectures. Examples of 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] Electronic device 412 typically includes a variety of computer system readable media. These media can be any available media that can be accessed by electronic device 412, including volatile and non-volatile media, removable and non-removable media.

[0125] 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. Electronic device 412 may further include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, storage system 434 may be used to read and write non-removable, non-volatile magnetic media (… Figure 16 Not shown; usually referred to as a "hard drive"). Although Figure 16 Not shown, a disk drive for reading and writing to a removable non-volatile disk (e.g., a "floppy disk") and an optical disc drive for reading and writing to a removable non-volatile optical disc (e.g., 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 bus 418 via one or more data media interfaces. 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 in, for example, a 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 an implementation of a network environment. Program modules 442 typically perform the functions and / or methods described in the embodiments of the present invention.

[0127] Electronic device 412 can also communicate with one or more external devices 414 (e.g., keyboard, pointing terminal, display 424, etc.), and with one or more terminals that enable a user to interact with the electronic device 412, and / or with any terminal that enables the electronic device 412 to communicate with one or more other computing terminals (e.g., network card, modem, etc.). This communication can be performed via input / output (I / O) interface 422. Furthermore, electronic device 412 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) via network adapter 420. 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.

[0128] The processor 416 executes various functional applications and data processing by running programs stored in the storage device 428, such as implementing the impedance model determination method for grid-connected inverters provided in this embodiment of the invention, which includes:

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

[0130] Based on grid connection parameters and grid connection structure information, the basic mathematical model of the grid-connected inverter is determined;

[0131] Based on the basic mathematical model and grid connection parameters, the small-signal impedance model of the grid-connected inverter is determined, and the continuous impedance model of the grid-connected inverter is determined based on the small-signal impedance model.

[0132] Based on grid connection parameters and grid connection structure information, and based on the discrete characteristics of the grid-connected inverter's control system, the hybrid small-signal model of the grid-connected inverter is determined, and based on the hybrid small-signal model, the hybrid impedance model of the grid-connected inverter is determined.

[0133] The target impedance model is determined based on the continuous impedance model and the mixed impedance model.

[0134] Example 5

[0135] Embodiment 5 of the present invention also provides a computer-readable storage medium storing a computer program thereon. When executed by a processor, the program implements the impedance model determination method for a grid-connected inverter as provided in the embodiments of the present invention. The method includes:

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

[0137] Based on grid connection parameters and grid connection structure information, the basic mathematical model of the grid-connected inverter is determined;

[0138] Based on the basic mathematical model and grid connection parameters, and based on the discrete characteristics of the grid-connected inverter's control system, the small-signal impedance model of the grid-connected inverter is determined, and the continuous impedance model of the grid-connected inverter is determined based on the small-signal impedance model.

[0139] Based on grid connection parameters and grid connection structure information and discrete characteristics, the hybrid small-signal model of the grid-connected inverter is determined, and based on the hybrid small-signal model, the hybrid impedance model of the grid-connected inverter is determined.

[0140] The target impedance model is determined based on the continuous impedance model and the mixed impedance model.

[0141] The computer storage medium of this invention can be any combination of one or more computer-readable media. A computer-readable medium can be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium can be, for example,—but not limited to—an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof. In this document, a computer-readable storage medium can 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] Computer-readable signal media may include data signals propagated in baseband or as part of a carrier wave, carrying computer-readable program code. Such propagated data signals may take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. Computer-readable signal media may also be any computer-readable medium other than computer-readable storage media, capable of sending, propagating, or transmitting programs for use by or in connection with an instruction execution system, apparatus, or device.

[0143] Program code contained on a computer-readable medium may be transmitted using any suitable medium, including—but not limited to—wireless, wire, optical fiber, RF, etc., or any suitable combination thereof.

[0144] Computer program code for performing the operations of this invention can be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, and C++, as well as conventional procedural programming languages ​​such as "C" or similar programming languages. The program code can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or terminal. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or can be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0145] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, rearrangements, combinations, and substitutions can be made without departing from the scope of protection 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, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for determining an impedance model of a grid-connected inverter, characterized in that, The method comprises the following steps: acquiring grid-connection parameters and grid-connection structure information of a grid-connection inverter; determining a basic mathematical model of the grid-connection inverter according to the grid-connection parameters and the grid-connection structure information; determining a small-signal impedance model of the grid-connection inverter according to the basic mathematical model and the grid-connection parameters, and determining a continuous impedance model of the grid-connection inverter according to the small-signal impedance model; determining a hybrid small-signal model of the grid-connection inverter according to the basic mathematical model and the grid-connection parameters, and based on discrete characteristics of a control system of the grid-connection inverter, and determining a hybrid impedance model of the grid-connection inverter according to the hybrid small-signal model; performing stability analysis on the grid-connection inverter based on the hybrid impedance model and the continuous impedance model; if the grid-connection inverter is unstable in operation, the grid-connection inverter is unstable in operation based on the hybrid impedance model, and the grid-connection inverter is stable in operation based on the continuous impedance model, then determining that a target impedance model is the hybrid impedance model. 2.The method for determining impedance model of 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-connection inverter, comprises the following steps: sampling continuous output voltage and output current of the grid-connection 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-connection inverter, to obtain discretized output voltage and output current; establishing the hybrid small-signal model according to the discretized output voltage and output current. 3.The method of claim 1, wherein, The step of determining the hybrid impedance model of the grid-connection inverter according to the hybrid small-signal model, comprises the following steps: determining an equivalent hybrid small-signal circuit according to the hybrid small-signal model; the equivalent hybrid small-signal circuit is a circuit comprising an inverter side and a grid side; determining an equivalent impedance of the grid-connection inverter according to the equivalent hybrid small-signal circuit, to determine the hybrid impedance model.

4. The method of claim 3, wherein, The step of determining the equivalent hybrid small-signal circuit according to the hybrid small-signal model, comprises the following steps: determining 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 of claim 3, wherein, The hybrid impedance model wherein, is the equivalent impedance, and are two parallel impedances on the inverter side in the equivalent hybrid small signal circuit, respectively. 6.The method for determining impedance model of grid-connected inverter according to claim 1, characterized in that, The step of determining the small-signal impedance model of the grid-connection inverter according to the basic mathematical model and the grid-connection parameters, comprises the following steps: determining a transfer function between grid-connection voltage disturbance and grid-connection current disturbance of the grid-connection inverter according to the basic mathematical model and the grid-connection parameters; determining the small-signal impedance model of the grid-connection inverter according to the basic mathematical model and the transfer function.

7. The method of claim 6, wherein, The step of determining the continuous impedance model of the grid-connection inverter according to the small-signal impedance model, comprises the following steps: determining output current disturbance of the grid-connection inverter according to the small-signal impedance model; determining an equivalent small-signal circuit according to the small-signal impedance model and the output current disturbance; the equivalent small-signal circuit is a circuit comprising an inverter side and a grid side; determining an equivalent impedance of the grid-connection inverter according to the equivalent small-signal circuit, to determine the continuous impedance model. 8.The method for determining impedance model of grid-connected inverter according to claim 1, characterized in that, The output voltage and the output current of the hybrid small signal model are in a functional relationship.

9. An impedance model determination apparatus of a grid-connected inverter, characterized by comprising: The method comprises the following steps: a parameter acquisition module, configured to acquire grid-connected parameters and grid-connected structure information of the grid-connected inverter; a basic model determination module, configured to determine a 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, configured to determine a small signal impedance model of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters, and determine a continuous impedance model of the grid-connected inverter according to the small signal impedance model; a hybrid model determination module, configured to determine a hybrid small signal model of the grid-connected inverter according to the basic mathematical model and the grid-connected parameters and based on discrete characteristics of a control system of the grid-connected inverter, and determine a hybrid impedance model of the grid-connected inverter according to the hybrid small signal model; a target model determination module, configured to determine a target impedance model according to the continuous impedance model and the hybrid impedance model; the target model determination module comprises: 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; a target model determination unit, configured to, if the grid-connected inverter is unstable in operation, determine that the grid-connected inverter is unstable in operation based on the hybrid impedance model and that the grid-connected inverter is stable in operation based on the continuous impedance model, and determine the target impedance model as the hybrid impedance model.

Images