Method for constructing multiplication element model and solving circuit network

Abstract

A method of constructing a multiplied element model and solving a circuit network is provided, the multiplied element comprising a current source at a first side and a voltage source at a second side, the method of constructing a multiplied element model comprising: determining a state variable, the state variables comprise node voltages of a first type of elements and a second type of elements and currents flowing through the second type of elements, the first type of elements are other elements except a voltage source in the multiplying elements, and the second type of elements are the voltage source in the multiplying elements; and constructing a multiplication element model based on the state variable and a nodal analysis method.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit simulation, and in particular to a method for constructing a multiplication element model and solving a circuit network. Background Art

[0002] As energy and environmental issues become increasingly prominent, new energy power generation systems such as wind power and photovoltaics have been widely used. Compared with traditional thermal power units, the capacity of a single new energy unit is usually much smaller than that of a large thermal power unit. Therefore, in actual systems, new energy stations are usually composed of dozens or even hundreds of units. Power electronic converters and other equipment are also widely used in various systems, with a large number of parallel units. However, the large-scale access of new energy units will affect the safe and stable operation of the power system. In order to ensure the power supply reliability of the power system, it is necessary to conduct dynamic safety assessments on power systems with large-scale access to new energy.

[0003] Circuit simulation based on computer software is an important tool for studying power systems and power electronic systems, including simulation methods based on node method and state space method. In power system simulation, time domain circuit simulation is often called electromagnetic transient simulation. If a detailed model of each unit is built in the simulation to form a new energy station model, the model will be very large and occupy too many computing resources, which greatly reduces the simulation efficiency. In order to balance the simulation accuracy and simulation efficiency, it is necessary to perform equivalent modeling of the new energy station according to the principle that the grid connection point has the same electrical quantity characteristics.

[0004] Traditional equivalent modeling methods include parameter equivalence and the use of multiplication elements. The essence of parameter equivalence is to use the capacity weighted method to perform equivalent calculations on the parameters of new energy units, and use a single unit or multiple units to simulate the output characteristics of the entire station. Among them, Reference 1 (Jurado F, García CA, Fernández LM, et al. Equivalent models of wind farms by using aggregated wind turbines and equivalent winds [J]. Energy conversion & management, 2009, 50 (3): 691-704.) uses a single-machine equivalent method to equate all wind turbines to one wind turbine, and proposes and compares two input wind speed equivalent methods; Reference 2 (You Chao. Research on wind farm equivalent method based on equivalent machine [D]. Harbin Institute of Technology, 2019.) combines the actual input power of the unit to calculate the equivalent unit parameters, thereby improving the equivalent accuracy.

[0005] The method of constructing a multiplication element does not require complex mathematical calculations and can reduce the calculation time compared to the parameter equivalent method. Currently, there are mainly two types: the controlled current source model with delay and the Bergeron model. The controlled current source model with delay uses a controlled current source at the grid connection point to realize current multiplication. The amplified current value is the simulation result of a step length on the detailed model branch to simulate the scenario of multiple new energy units connected to the grid in parallel. This method has a simple structure, but because the power electronic circuit contains a large number of harmonics, they are amplified by the current source along with the fundamental wave, and a step length delay is introduced. Harmonics will not only cause the voltage and current in the grid to be polluted, but the voltage and current containing a large number of harmonics will also affect the operation of the control circuit in turn, and ultimately affect the normal operation of the new energy unit, which is easy to cause system instability. Therefore, it is necessary to design an appropriate filter function to eliminate system harmonics, and the introduction of the filter function will lead to a significant decrease in calculation accuracy.

[0006] The principle based on the equivalence of the Bergeron model is to use an ideal lossless transmission line model for modeling, and to represent the multiplied component as an ideal lossless distributed parameter branch. Through the transmission line model, the current can be amplified to n times the original value and connected to the power grid, realizing the equivalent modeling of large-scale stations. However, if the set transmission line length is much larger than the transmission line length in the actual circuit, this method will introduce additional impedance of the non-existent transmission line, mainly including series inductance and capacitance to ground, thereby changing the impedance characteristics of the system and causing the original resonant frequency point to change.

[0007] Therefore, a method of constructing multiplication elements with small error, high accuracy and simple calculation is needed to perform equivalent modeling of new energy stations. Summary of the invention

[0008] Based on the above problems in the prior art, the present invention provides a method for constructing a multiplication element model, wherein the multiplication element includes a current source located on a first side and a voltage source located on a second side, and the method includes:

[0009] Determine state variables, the state variables including node voltages of first-type elements and second-type elements and currents flowing through second-type elements, wherein the first-type elements are elements other than voltage sources in the multiplication elements, and the second-type elements are voltage sources in the multiplication elements; and

[0010] A multiplication element model is constructed based on the state variables and the node analysis method.

[0011] In one embodiment, the step of constructing a multiplication element model based on the state variables and the node analysis method further includes:

[0012] Based on the node analysis method, obtaining the constraint equations of the first type of components and the second type of components;

[0013] Based on Kirchhoff's current law equation and Kirchhoff's voltage law equation and the constraint equation, a multiplication element model is obtained.

[0014] In one embodiment, the multiplying element comprises a first side and a second side,

[0015] The first side includes: a current source, a first node connected to the positive electrode of the current source, and a second node connected to the negative electrode of the current source;

[0016] The second side includes: a voltage source, a third node connected to the positive electrode of the voltage source, and a fourth node connected to the negative electrode of the voltage source;

[0017] The voltage difference between the third node and the fourth node is m times the voltage difference between the first node and the second node, and the current flowing through the current source is n times the current flowing through the voltage source, wherein m and n are both greater than 0.

[0018] In one embodiment, the multiplication element model is:

[0019]

[0020] Among them, V x + is the first node voltage, V x - is the second node voltage, V y + is the third node voltage, V y - is the fourth node voltage, I y is the current flowing through the voltage source.

[0021] In one embodiment, the state variable is I y .

[0022] In one embodiment, both the current source and the voltage source are controlled sources.

[0023] The present invention also provides a method for solving a circuit network, comprising:

[0024] The multiplication element model is substituted into the entire circuit network simulation model, and the entire circuit network is solved to obtain the voltage and current values ​​of each node in the circuit.

[0025] In one embodiment, the method for solving the circuit network further includes:

[0026] Obtaining a coefficient matrix of a multiplication element based on the multiplication element model;

[0027] The coefficient matrices of the multiplication elements are sequentially added to the circuit network matrix to solve the circuit network.

[0028] The present invention also provides a computer-readable storage medium, characterized in that a computer program is contained thereon, and the computer program can be executed by a processor to implement the steps of the above method.

[0029] The present invention further provides an electronic device, characterized in that it comprises:

[0030] one or more processors; and

[0031] A memory for storing one or more executable instructions;

[0032] The one or more processors are configured to implement the steps of the above method by executing the one or more executable instructions.

[0033] The method of constructing a multiplication element model and solving a circuit network of the present invention can simultaneously solve the electrical quantities on both sides of the multiplication element within the same time step, avoiding the introduction of any additional errors other than computer numerical calculation errors, and realizing accurate calculation and updating of electrical quantities. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FIG. 4 shows a time domain equivalent circuit diagram of a multiplication element according to an embodiment of the present invention.

[0035] Figure 2 A flow chart of a method for constructing a multiplication element based on a controlled source model according to an embodiment of the present invention is shown.

[0036] Figure 3 A schematic diagram showing a multiplication element used in a direct-drive wind turbine grid-connected model according to an embodiment of the present invention is shown.

[0037] Figure 4 A schematic diagram showing a multiplication element used in a doubly-fed wind turbine grid-connected model according to an embodiment of the present invention is shown.

[0038] Figure 5 A schematic diagram showing a multiplication element used in a photovoltaic grid-connected model according to an embodiment of the present invention is shown.

[0039] Figure 6 A schematic diagram showing the use of a multiplying element in an energy storage grid-connected model according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be noted that the embodiments given in the present invention are only for illustration and do not limit the protection scope of the present invention.

[0041] The multiplication element in the prior art only includes a current source, which has large errors and low precision. The present invention proposes a new multiplication element and a method for constructing a multiplication element model. By including a voltage source in the multiplication element and using the current flowing through the voltage source as a state variable, the obtained multiplication element model can avoid introducing any additional errors other than computer numerical calculation errors (such as truncation errors, rounding errors, etc.), thereby achieving accurate calculation and update of electrical quantities.

[0042] Figure 1 FIG. 1 shows a time domain equivalent circuit diagram of a multiplication element according to an embodiment of the present invention. The multiplication element 100 includes a first side S1 and a second side S2. The first side S1 includes a current source 10, a first node 11 connected to the positive electrode of the current source 10, and a second node 12 connected to the negative electrode of the current source 10. The voltage of the first node 11 is V x + , the voltage of the second node 12 is V x - , the node voltage difference between the first node 11 and the second node 12 is V x , that is, V x + -V x - , the node current flowing through the current source 10 is I x The second side S2 includes a voltage source 20, a third node 23 connected to the positive electrode of the voltage source 20, and a fourth node 24 connected to the negative electrode of the voltage source 20. The voltage of the third node 23 is V y + , the voltage of the fourth node 24 is V y - , the node voltage difference between the third node 23 and the fourth node 24 is V y , that is, V y + -V y - , the node current flowing through the voltage source 20 is I y The current source 10 and the voltage source 20 are both controlled sources, and their voltage or current is controlled by the voltage or current of other parts in the circuit. The voltage difference V between the nodes of the second side S2 of the multiplication element 100 is y is the voltage difference V between nodes of the first side S1 x m times, that is, V y =mV x, the node current I of the first side S1 x is the inter-node current I of the second side S2 y n times, that is, I x =nI y , so the power P of the first side S1 x is the power P of the second side S2 y n / m times, wherein m and n are both greater than 0, and preferably m and n are both positive integers. By setting the values ​​of m and n, the purpose of power multiplication can be achieved. Wherein, based on the different values ​​of m and n, the first side can be the side before multiplication or the side after multiplication.

[0043] Those skilled in the art should understand that Figure 1 The multiplication elements shown in are only examples and do not constitute a limitation to the present invention. In one embodiment, the first side S1 may include multiple current sources, and the second side S2 may also include multiple voltage sources; in another embodiment, the first side S1 may include multiple voltage sources, and the second side S2 may also include multiple current sources.

[0044] Figure 2 A flow chart of a method for constructing a multiplication element based on a controlled source model according to an embodiment of the present invention is shown. The method comprises:

[0045] Step 201: Determine state variables, which include node voltages of first-type elements and second-type elements and currents flowing through second-type elements, wherein first-type elements are elements other than voltage sources in the multiplication elements, and second-type elements are voltage sources in the multiplication elements.

[0046] The traditional node analysis method uses node voltage as the state variable, and the equation of any element is shown in equation (1):

[0047] i=Yu+s (1)

[0048] Where i is the branch current, u is the node voltage, s is the current of an independent current source or a controlled current source, and Y is the admittance matrix, which is a matrix composed of the conductance values ​​(or resistance and admittance values) between each node in the circuit.

[0049] However, since there is a voltage source branch (including an independent voltage source and a controlled voltage source) in the multiplication element circuit of the present invention, the branch impedance is infinite, and the element equation is difficult to convert into the form of equation (1). When using a computer to solve the network equation, the node analysis method cannot be used directly to construct the equation. Therefore, it is necessary to improve the traditional node analysis method to construct a multiplication element equation suitable for computer solution.

[0050] In the multiplication element construction method of the present invention, the number of state variables is increased. In addition to the original node voltage, the current flowing through the voltage source element is added as a state variable, that is, the state variables of the present invention include the node voltages of the first type of element and the second type of element and the current flowing through the second type of element.

[0051] Step 202: Construct a multiplication element model based on state variables and node analysis method.

[0052] First, the components are divided into two categories: the first category is other components except voltage sources, and the second category is voltage sources. Based on the node analysis method, the constraint equations of these two types of components can be expressed as follows:

[0053] i1+Z 12 i2=Y 11 u1+Y 12 u2+e1 (2)

[0054] Z 22 i2=Y 21 u1+Y 22 u2+e2 (3)

[0055] Among them, i1 is the current flowing through the first type of element, i2 is the current flowing through the second type of element, u1 is the node voltage of the first type of element, u2 is the node voltage of the second type of element, Y 11 is the self-admittance matrix of the first type element, Y 22 is the self-admittance matrix of the second type element, Y 12 and Y 21 is the mutual admittance matrix between the first type of element and the second type of element, Z 12 is the mutual impedance matrix between the first type of element and the second type of element, Z 22 is the impedance matrix of the second type of element, e1 is the historical quantity of the first type of element, and e2 is the historical quantity of the second type of element, where the historical quantity refers to the calculation result of the previous step in the simulation calculation.

[0056] The Kirchhoff's current law (KCL) equation expressed by the correlation matrix A is:

[0057] A1i1+A2i2=0 (4)

[0058] The Kirchhoff voltage law (KVL) equation expressed by the correlation matrix A is:

[0059]

[0060]

[0061] Among them, v is the node voltage, A1 is the correlation matrix of the first type of components, and A2 is the correlation matrix of the second type of components.

[0062] Substituting formula (4), (5), and (6) into formula (2) and (3), we obtain:

[0063]

[0064]

[0065] Written in matrix form:

[0066]

[0067] In one embodiment, Figure 1 The multiplication element shown in FIG. 1 is used as an example for detailed description, wherein the first type of element is a current source and the second type of element is a voltage source. The first node voltage V x + , the second node voltage V x - , the third node voltage V y + , the fourth node voltage V y - The node voltages of the first and second type components, the node current I y The current flowing through the second type of element, that is, the state variable is I y . Combined Figure 1 The multiplication element structure shown in FIG. 1 and the matrix form equation of the multiplication element 100 obtained from the above formulas (2) to (9) are:

[0068]

[0069] Formula (10) is Figure 1 The multiplication element model of the multiplication element 100 shown. The values ​​of the empty positions in formula (10) are all 0. If the formula is solved for the multiplication element alone, the obtained node voltage and current values ​​are all 0. However, in practical applications, when the multiplication element model is substituted into the entire circuit network simulation model, the blank positions of formula (10) will be filled based on the entire circuit network, and the corresponding voltage and current values ​​can be solved at this time. It can be seen from formula (10) that the multiplication element model can simultaneously solve the electrical quantities on both sides of the multiplication element within the same time step, avoiding the introduction of any additional errors other than computer numerical calculation errors (such as truncation errors, rounding errors, etc.), and realizing accurate calculation and updating of electrical quantities. The present invention is not limited to the form of the above-mentioned multiplication element 100. Based on the above teachings, those skilled in the art can also conceive other forms of multiplication elements and obtain their multiplication element models.

[0070] The present invention also provides a method for solving a circuit network based on the multiplication element model, which comprises the following steps:

[0071] Step 203: Substitute the multiplication element model into the entire circuit network simulation model, and solve the entire circuit network to obtain the voltage value and current value of each node in the circuit.

[0072] The entire circuit simulation model refers to a simulation model including new energy, converters, transformers and power grids, and a circuit simulation model known in the prior art may be used.

[0073] The multiplication element model proposed in the present invention can be applied to any method for solving circuit networks, including but not limited to the forward Euler method, the backward Euler method, the trapezoidal method, the Newton iteration method, the state space method, etc.

[0074] In one embodiment, the circuit network simulation model is in the form of a circuit network matrix, and the multiplication element model can be added to the circuit network matrix in the form of a matrix for solving. Taking the multiplication element in formula (10) as an example, step 203 is described in detail, which includes the following steps:

[0075] Step 2031: Obtain the coefficient matrix of the multiplication element based on the multiplication element model, according to V x + ,V x - ,V y + ,V y - ,I y The order of , the coefficient matrix is ​​shown in Table 1:

[0076] Table 1 Multiplication element coefficient matrix

[0077]

[0078] Step 2032: Add the coefficient matrix of the multiplication element to the circuit network matrix in order to solve the circuit network.

[0079] The multiplication element model proposed in the present invention is applicable to all converter models in new energy systems and other electrical systems, including a two-resistance model, a constant impedance model, a switching function model, an average value model, and improved models based on the above models.

[0080] The multiplying element model proposed in the present invention is applicable to all topological structures in new energy systems and other electrical systems, including the uncontrolled rectifier topology of the direct-drive wind turbine model, the fully controlled rectifier model and the BOOST boost circuit combined topology, the PMSG parallel converter topology, the PMSG multi-phase converter topology, the back-to-back converter model topology of the doubly fed wind turbine, the unipolar converter topology of the photovoltaic system, and the two-stage topology combining the BOOST boost circuit and the converter model.

[0081] The multiplication element model proposed in the present invention can be placed between the new energy system and the transformer, or between the transformer and the power grid model, or placed in parallel with the same unit according to the circuit topology principle.

[0082] Figure 3 A schematic diagram showing a multiplication element used in a direct-drive wind turbine grid-connected model according to an embodiment of the present invention is shown. Figure 4 A schematic diagram showing a multiplication element used in a doubly-fed wind turbine grid-connected model according to an embodiment of the present invention is shown. Figure 5 A schematic diagram showing a multiplication element used in a photovoltaic grid-connected model according to an embodiment of the present invention is shown. Figure 6 A schematic diagram showing the use of a multiplying element in an energy storage grid-connected model according to an embodiment of the present invention is shown.

[0083] The multiplication element, the method for constructing the multiplication element model and the method for solving the circuit network of the present invention can reduce the computational complexity of the large-scale new energy grid-connected system model, solve the problem of errors in the existing multiplication element, and improve the computational accuracy of the simulation calculation. The method proposed by the present invention uses controlled sources at both ends of the multiplication element to realize the multiplication function, uses the improved MNA method to construct the matrix equation of the multiplication element, and adds it to the solution matrix of the circuit, so as to achieve the purpose of solving the electrical quantities on both sides of the multiplication element at the same time step, avoid introducing any additional errors other than computer numerical calculation errors (such as truncation errors, rounding errors, etc.), and realize accurate calculation and update of electrical quantities.

[0084] The present invention can use one unit at the grid connection point to simulate the external equivalent characteristics of multiple units in a new energy station, and use multiplication elements to achieve equivalent modeling of the new energy station. The present invention is also applicable to other scenarios where a large number of parallel devices with the same structure need to be equivalently modeled. Using the multiplication element model proposed in the present invention to perform electromagnetic transient simulation, the obtained characteristics are the same as the simulation results obtained by connecting multiple new energy unit models in parallel, which improves the simulation accuracy and efficiency of large-scale new energy grid-connected systems.

[0085] Although the present invention has been described through preferred embodiments, the present invention is not limited to the embodiments described herein but includes various changes and modifications that may be made without departing from the scope of the present invention.

Claims

1. A method for constructing a multiplication element model, wherein the multiplication element includes a current source located on a first side and a voltage source located on a second side, the method comprising: Determine state variables, the state variables including node voltages of first-type elements and second-type elements and currents flowing through second-type elements, wherein the first-type elements are elements other than voltage sources in the multiplication elements, and the second-type elements are voltage sources in the multiplication elements; and A multiplication element model is constructed based on the state variables and the node analysis method.

2. The method for constructing a multiplication element model according to claim 1, wherein: The step of constructing a multiplication element model based on the state variables and the node analysis method also includes: Based on the node analysis method, obtaining the constraint equations of the first type of components and the second type of components; Based on Kirchhoff's current law equation and Kirchhoff's voltage law equation and the constraint equation, a multiplication element model is obtained.

3. The method for constructing a multiplication element model according to claim 1, wherein: The multiplying element comprises a first side and a second side, The first side includes: a current source, a first node connected to the positive electrode of the current source, and a second node connected to the negative electrode of the current source; The second side includes: a voltage source, a third node connected to the positive electrode of the voltage source, and a fourth node connected to the negative electrode of the voltage source; The voltage difference between the third node and the fourth node is m times the voltage difference between the first node and the second node, and the current flowing through the current source is n times the current flowing through the voltage source, wherein m and n are both greater than 0.

4. The method for constructing a multiplication element model according to claim 3, wherein: The multiplication element model is: Among them, V x + is the first node voltage, V x - is the second node voltage, V y + is the third node voltage, V y - is the fourth node voltage, I y is the current flowing through the voltage source.

5. The method for constructing a multiplication element model according to claim 4, wherein: The state variable is I y .

6. The method for constructing a multiplication element model according to claim 1, wherein: The current source and the voltage source are both controlled sources.

7. A method for solving a circuit network, comprising: Substitute the multiplication element model described in any one of claims 1 to 6 into the entire circuit network simulation model, and solve the entire circuit network to obtain the voltage value and current value of each node in the circuit.

8. The method for solving a circuit network according to claim 7, further comprising: Obtaining a coefficient matrix of a multiplication element based on the multiplication element model; The coefficient matrix of the multiplication elements is sequentially added to the circuit network matrix to solve the circuit network.

9. A computer-readable storage medium, characterized in that: A computer program is included thereon, and the computer program can be executed by a processor to implement the steps of the method according to any one of claims 1 to 8.

10. An electronic device, characterized in that: include: one or more processors; as well as A memory for storing one or more executable instructions; The one or more processors are configured to implement the steps of the method of any one of claims 1-8 by executing the one or more executable instructions.

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