Dynamic complex power angle model and control method of network-forming inverter

Abstract

The invention discloses a dynamic complex power angle model and a control method of a network-forming inverter, relates to the field of network-forming inverters, and aims to simplify a decoupling control design process and improve control efficiency by establishing a novel dynamic complex power angle model and a control strategy, and more accurately and quickly respond to power grid fluctuation so as to improve the reliability of the network-forming inverter. The overall stability and response speed of a power system are enhanced, and powerful technical support is provided for constructing a more intelligent, efficient and stable green power grid.

Description

Technical Field

[0001] The present invention relates to the field of grid-type inverters, and in particular to a dynamic complex power angle model and a control method of a grid-type inverter. Background Art

[0002] Grid-forming factor (GFM) control is a technique that replaces grid-following control in grid-connected inverters. It has attracted widespread interest from scholars around the world. GFM inverters operate as voltage sources connected to the grid, with robust small-signal stability and grid-forming capabilities. Recently, many GFM control schemes have been proposed, such as traditional droop control, virtual synchronous generator (VSG) control, power synchronization control (PSC), synchronous power control (SPC), and multivariable feedback GFM control (MFC). The above grid-forming factor control is designed to be widely applied to the field of power systems that are highly dependent on renewable energy, including multiple key links from renewable energy grid connection control to microgrid operation and management, to power market transaction assistance, power system planning and design, and even rapid grid restoration in emergency situations.

[0003] Conventional droop, VSG, PSC, and SPC control methods use transfer function models to design ideal damping and settling time for GFM (Grid Forming Inverter) power control. The above GFM control methods control active power and reactive power separately based on real variable (RV) models. Therefore, the system is modeled as a dual-input dual-output (DIDO) system, where the inputs are phase angle and amplitude, and the outputs are active power and reactive power. Therefore, this model is called phase-amplitude-active-reactive power model. In this case, multivariable design and higher system order need to be considered compared to single-input single-output (SISO) system. In three-phase systems, complex variable (CV) control is usually used to reduce the system order and handle coupling terms. Therefore, CV-based control has been successfully applied to inverter current and voltage control and grid synchronization. However, due to the asymmetry of active power and reactive power, the complex variable model and control of power synchronization GFM control have not been fully developed.

[0004] Before the control design of GFM inverter power control is performed, a complex power model should be established first. Recently, a complex-valued droop control has been designed for a single inverter. However, the output of the complex-valued droop controller is the reference of the dq voltage control loop, not the frequency, because the phase angle difference is replaced by the q-axis voltage. In addition, there is a complex-valued droop controller for the voltage control loop in the αβ framework. This controller uses frequency as the control variable, but the parameters of the active and reactive power loops are still designed separately.

[0005] The above traditional grid-based control faces challenges to power system stability brought by renewable energy, especially in dealing with complex working conditions, where there are limitations, including the complexity of power control and power coupling.

[0006] Therefore, in order to extend the CV application to GFM control, a CPPA model is first established. Based on the proposed dynamic CPPA model, a GFM power control strategy is designed to transform the system into a single-input single-output (SISO) system, which reduces the design difficulty of the system and improves the control performance of the system. Summary of the invention

[0007] The object of the present invention is to provide a dynamic power-complexing angle model and control method for a grid-connected inverter, so as to solve the problems raised in the above-mentioned background technology.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] A dynamic complex power angle model and control method of a grid-connected inverter. Step 1: Establish a dynamic complex model of a GFM inverter.

[0010] The general control target of GFM power control can be simplified to impedance In a dual-bus system, one of the buses is generally a controllable GFM voltage source with adjustable frequency and amplitude. In order to unify the design of active power controller (APC) and reactive power controller (RPC), a dynamic CPPA model of GFM inverter is established in this paper. The complex power between the two buses can be expressed as:

[0011] s=p+jq=u1i * #(1)

[0012] Where p and q are active power and reactive power respectively, u1 and i are the voltage and current at the PCC (Point of Common Coupling) point.

[0013] By taking the derivative of the complex power, we have:

[0014]

[0015] Where L and R are the inductance and resistance of the L line, u2 is the grid voltage, and “*” represents the conjugate of the complex variable.

[0016] make According to complex number operations, we have:

[0017]

[0018] definition:

[0019]

[0020] Formula (2) can be rewritten in matrix form:

[0021]

[0022] Then, enter u p and u q The small signal can be processed as:

[0023]

[0024] Among them, Δθ=θ1-θ2=Δθ1-Δθ2 represents the phase difference, and "Δ" also represents the small signal disturbance.

[0025] In this case, the vector [Δu p Δu q ] T It can be written as the complex variable Δu s =Δu p +jΔu q The form of. Equation (6) becomes:

[0026]

[0027] in:

[0028]

[0029] Finally, we get:

[0030]

[0031] In general, the phase difference between the two voltage sources is small, and the amplitude difference is usually less than 10%. s1 In comparison, s2 can be ignored. Finally, the complex power angle transfer function of the grid-connected inverter can be obtained as follows:

[0032]

[0033] Where k2 and k3 are equivalent complex coefficients.

[0034] Step 2: Design the complex power controller for the GFM inverter.

[0035] From step 1, formula (10), we can get the complex power angle transfer function of the grid-connected inverter, G CPC (s) = k1G c (s) / s (k1 is the complex power controller gain coefficient) is the complex power controller that needs to be designed in the future, so that the complex power model of the GFM inverter can be established. In this case, the system can be designed through the SISO transfer function. cThe design is flexible and takes into account the traditional swing equation based controller.

[0036]

[0037] Where J is the moment of inertia, D is the damping coefficient, and w0 is the rated angular frequency.

[0038] Then, the closed-loop transfer function can be derived as:

[0039]

[0040] According to (12), the control parameters can be designed.

[0041] Compared with the prior art, the beneficial effects of the present invention are: by establishing a novel dynamic complex power angle model and control strategy, not only the decoupling control design process is simplified and the control efficiency is improved, but also the power grid fluctuation can be responded to more accurately and quickly, and the overall stability and response speed of the power system are enhanced, providing strong technical support for building a more intelligent, efficient and stable green power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the circuit diagram of the GFM inverter connected to the grid.

[0043] Figure 2 It is a control block diagram of complex power control based on CPPA. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] See also Figures 1-2 In an embodiment of the present invention, a dynamic complex power angle model and control method of a grid-connected inverter are provided. Step 1: Establish a dynamic complex model of a GFM-controlled grid-connected inverter.

[0046] The general control target of GFM power control can be simplified to impedance In general, one of the buses is a controllable GFM voltage source with adjustable frequency and amplitude. In order to unify the design of active power controller (APC) and reactive power controller (RPC), a dynamic CPPA model of GFM inverter is established in this paper. The complex power between the two buses can be expressed as:

[0047] s=p+jq=u1i* #(1)

[0048] Where p and q are active power and reactive power respectively, u1 and i are the voltage and current at the PCC (Point of Common Coupling) point.

[0049] By taking the derivative of the complex power, we have:

[0050]

[0051] Where L and R are the inductance and resistance of the L line, u2 is the grid voltage, and “*” represents the conjugate of the complex variable.

[0052] make According to complex number operations, we have:

[0053]

[0054] definition:

[0055]

[0056] Formula (2) can be rewritten in matrix form:

[0057]

[0058] Then, enter u p and u q The small signal can be processed as:

[0059]

[0060] Among them, Δθ=θ1-θ2=Δθ1-Δθ2 represents the phase difference, and "Δ" also represents the small signal disturbance.

[0061] In this case, the vector [Δu p Δu q ] T It can be written as the complex variable Δu s =Δu p +jΔu q The form of. Equation (6) becomes:

[0062]

[0063] in:

[0064]

[0065] Finally, we get:

[0066]

[0067] In general, the phase difference between the two voltage sources is small, and the amplitude difference is usually less than 10%. s1 In comparison, s2 can be ignored. Finally, the complex power angle transfer function of the grid-connected inverter can be obtained as follows:

[0068]

[0069] Where k2 and k3 are equivalent complex coefficients.

[0070] Step 2: Design the complex power controller for the GFM inverter.

[0071] From step 1, formula (10), we can get the complex power angle transfer function of the grid-connected inverter, G CPC (s) = k1G c (s) / s (k1 is the complex power controller gain coefficient) is the complex power controller that needs to be designed in the future, so that the complex power model of the GFM inverter can be established. In this case, the system can be designed through the SISO transfer function. c The design is flexible and takes into account the traditional swing equation based controller.

[0072]

[0073] Where J is the moment of inertia, D is the damping coefficient, and w0 is the rated angular frequency.

[0074] Then, the closed-loop transfer function can be derived as:

[0075]

[0076] According to (12), the control parameters can be designed.

[0077] Point to be protected:

[0078] Step 1: Establish a dynamic complex model of the GFM-controlled grid-connected inverter.

[0079] The general control target of GFM power control can be simplified to impedance In general, one of the buses is a controllable GFM voltage source with adjustable frequency and amplitude. In order to unify the design of active power controller (APC) and reactive power controller (RPC), a dynamic CPPA model of GFM inverter is established in this paper. The complex power between the two buses can be expressed as:

[0080] s=p+jq=u1i * #(1)

[0081] Where p and q are active power and reactive power respectively, u1 and i are the voltage and current at the PCC (Point of Common Coupling) point.

[0082] By taking the derivative of the complex power, we have:

[0083]

[0084] Where L and R are the inductance and resistance of the L line, u2 is the grid voltage, and “*” represents the conjugate of the complex variable.

[0085] make According to complex number operations, we have:

[0086]

[0087] definition:

[0088]

[0089] Formula (2) can be rewritten in matrix form:

[0090]

[0091] Then, enter u p and u q The small signal can be processed as:

[0092]

[0093] Among them, Δθ=θ1-θ2=Δθ1-Δθ2 represents the phase difference, and "Δ" also represents the small signal disturbance.

[0094] In this case, the vector [Δu p Δu q ] T It can be written as the complex variable Δu s =Δu p +jΔu q The form of. Equation (6) becomes:

[0095]

[0096] in:

[0097]

[0098] Finally, we get:

[0099]

[0100] In general, the phase difference between the two voltage sources is small, and the amplitude difference is usually less than 10%.s1 In comparison, s2 can be ignored. Finally, the complex power angle transfer function of the grid-connected inverter can be obtained as follows:

[0101]

[0102] Where k2 and k3 are equivalent complex coefficients.

[0103] Step 2: Design the complex power controller for the GFM inverter.

[0104] From step 1, formula (10), we can get the complex power angle transfer function of the grid-connected inverter, G CPC (s) = k1G c (s) / s (k1 is the complex power controller gain coefficient) is the complex power controller that needs to be designed in the future, so that the complex power model of the GFM inverter can be established. In this case, the system can be designed through the SISO transfer function. c The design is flexible and takes into account the traditional swing equation based controller.

[0105]

[0106] Where J is the moment of inertia, D is the damping coefficient, and w0 is the rated angular frequency.

[0107] Then, the closed-loop transfer function can be derived as:

[0108]

[0109] According to (12), the control parameters can be designed.

[0110] 1. Example

[0111] Step 1: Establish a dynamic complex model of the GFM-controlled grid-connected inverter.

[0112] Figure 1 The grid-connected GFM inverter circuit is shown. The general control target of GFM power control can be simplified to impedance Dual bus systems such as Figure 1 As shown. Generally speaking, one of the buses is a controllable GFM voltage source with adjustable frequency and amplitude. In order to uniformly design the active power controller (APC) and reactive power controller (RPC), this paper establishes a dynamic CPPA model of the GFM inverter. Figure 1 As shown, the complex power between the two buses can be expressed as:

[0113] s=p+jp=u1i * #(1)

[0114] Where p and q are active power and reactive power respectively.

[0115] By taking the derivative of the complex power, we have:

[0116]

[0117] Where "*" represents the conjugate of a complex variable. According to complex number operations, we have:

[0118]

[0119] definition:

[0120]

[0121] Formula (2) can be rewritten in matrix form:

[0122]

[0123] Then, enter u p and u q The small signal can be processed as:

[0124]

[0125] Among them, Δθ=θ1-θ2=Δθ1-Δθ2 represents the phase difference, and "Δ" also represents the small signal disturbance.

[0126] In this case, the vector [Δu p Δu q ] T It can be written as the complex variable Δu s =Δu p +jΔu q The form of. Equation (6) becomes:

[0127]

[0128] in:

[0129]

[0130] Finally, we get:

[0131]

[0132] In general, the phase difference between the two voltage sources is small, and the amplitude difference is usually less than 10%. s1 In comparison, s2 can be ignored. Finally, the complex power angle transfer function of the grid-connected inverter can be obtained as follows:

[0133]

[0134] Where k2 and k3 are equivalent complex coefficients.

[0135] Step 2: Design the complex power controller for the GFM inverter.

[0136] Figure 2 The control block diagram of the complex power control based on CPPA is shown. CPC (s) = k1G c (s) / s (k1 is the complex power controller gain coefficient) is the complex power controller that needs to be designed in the future. In this case, the system can be designed by the SISO transfer function. c The design is flexible and takes into account the traditional swing equation based controller.

[0137]

[0138] Where J is the moment of inertia, D is the damping coefficient, and w0 is the rated angular frequency.

[0139] Then, the closed-loop transfer function can be derived as:

[0140]

[0141] According to (12), the control parameters can be designed.

[0142] The working principle of the present invention is:

[0143] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0144] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A dynamic power angle model and control method for a grid-connected inverter, characterized in that: The steps include: Step 1: Establish a dynamic complex model of the GFM inverter; The general control target of GFM power control is simplified to impedance In a dual-bus system, one bus is a controllable GFM voltage source with adjustable frequency and amplitude. The complex power between the two buses is expressed as: s=p+jq=u1i*#(1) Where p and q are active power and reactive power respectively, u1 and i are the voltage and current at the PCC (Point of Common Coupling); By taking the derivative of the complex power, we have: Where L and R are the inductance and resistance of the L line, u2 is the grid voltage, and "*" represents the conjugate of the complex variable; make According to complex number operations, we have: definition: Formula (2) is rewritten in matrix form: Then, enter u p and u q The small signal is processed as: Where Δθ=θ1-θ2=Δθ1-Δθ2 represents the phase difference, and "Δ" also represents the small signal disturbance; In this case, the vector [Δu p Δu q ] T Written as a complex variable Δu s =Δu p +jΔu q In the form of, equation (6) becomes: in: Finally, we get: The phase difference between the two voltage sources is small, so s1 In comparison, s2 Ignore, finally, the complex power angle transfer function of the grid-connected inverter is obtained as follows: Among them, k2 and k3 are equivalent complex coefficients; Step 2: Design the complex power controller of the GFM inverter; The complex power angle transfer function of the grid-connected inverter is obtained from formula (10) in step 1, G CPC (s) = k1G c (s) / s, k1 is the gain coefficient of the complex power controller, which is the complex power controller that needs to be designed in the future, so as to establish the complex power model of the GFM inverter: Where J is the moment of inertia, D is the damping coefficient, and w0 is the rated angular frequency; Then, the closed-loop transfer function is derived as: According to (12), design the control parameters.

Images